On Wednesday, November 9, 2022 at 6:16:40 PM UTC-5, peterwezeman@hotmail.com wrote:
> On Wednesday, November 9, 2022 at 2:22:01 PM UTC-6, David Brown wrote:

> I have found _Physics: volume 1_ by Robert Resnick, David Halliday, and Kenneth Krane to be useful. The first
> chapter is a good introduction to dimensions. Chapter 2 covers motion with constant acceleration.

I second that. It's a very good high school text. Some universities used to use it as a first year text.

William Hyde

On Thursday, November 10, 2022 at 8:38:11 AM UTC-6, Wolffan wrote:
> On 10 Nov 2022, David Brown wrote
> (in article<657e2ac8-4184-43f2...@googlegroups.com>):
> > On Wednesday, November 9, 2022 at 4:21:59 PM UTC-7, Wolffan wrote:
> > > On 09 Nov 2022, David Brown wrote
> > > (in article<d672798f-3b06-4d93...@googlegroups.com>):
> > > > Here's something I've been working on for a retro future project with hard
> > > > sci fi elements. It calls for a gigantic 300+ meter ship
> > > that’s aircraft carrier size. I hope that you’re starting from orbit, or
> > > there’s likely to be a problem.
> > >
> > > Also, that’s one dimension. What shape is it? It’s one thing if it’s a
> > > 300 metre long cylinder, with a diameter of, oh, 30 metres. It’s something
> > > else if it’s a 30-metre thick disk with a diameter of 300 metres. It’s a
> > > whole other thing if it’s a 300-metre radius sphere.
> > > > to accelerate to
> > > > 250,000 miles
> > > 250,000 miles per what?
> > > > for a trip to the outer solar system, which I arm waved to
> > > > maybe +12,000 miles of acceleration per day.
> > > you don’t do acceleration in miles per day. Personally, I work best in SI
> > > units: metres, kilogrammes, seconds, joules, watts, newtons, that kind of
> > > thing. The acceleration due to gravity, one gee, is approximately 9.81
> > > metres
> > > per second per second. (that last ‘per second’ is kind of important) One
> > > gee is a rather significant acceleration. I usually just round up to a nice
> > > even 10 m/s/s, it’s easier to work with.
> > >
> > > Some basic concepts:
> > >
> > > delta-vee is the total mission change in velocity. It’s rather
> > > significant.
> > >
> > > the mission delta-vee for a rocket-propelled vehicle is equal to the
> > > rocket's
> > > exhaust velocity times the natural log of the mass ratio, where the mass
> > > ratio is the total mass of rocket, payload, reaction mass, and everything
> > > else at the start of the flight (m1) divided my the mass of whatever is left
> > > at the end of the flight (m2). Note that that’s for the _total_ mission,
> > > you usually need to get there and back.
> > >
> > > v = u + at. That is, the final velocity equals the intial velocity plus the
> > > acceleration times the time spent under acceleration.
> > >
> > > s = ut + 0.5at^2. That is, the displacement equals the inital velocity times
> > > the time under acceleration plus half the acceleration times the square of
> > > the time.
> > >
> > > So let’s do an example: we want to go to the Moon. We want to do it at one
> > > gee continuous accel. We want to get back.
> > >
> > > So... the distance from the Earth to the Moon is 380,000 kilomtres, or 380
> > > million mtres. That’s 3.8 x 10^8 metres. We have to get there and back.
> > > That’s 7.6 x 10^8 metres. (It’s not really 380 million metres. See
> > > below)
> > >
> > > Ok... problem. We need to arrive at the Moon with velocity of zero relative
> > > to the Moon. We need to get back to Earth, or at least Earth orbit, with
> > > velocity zero. (well, we have to make lunar orbit and Earth orbit, but we
> > > can
> > > worry about that later.) This means that we can’t just boost all the way,
> > > we must boost half way, turn around, slow down. We must do this twice to
> > > make
> > > the round trip. As we need to fiddle around a little, let’s say that
> > > it’s
> > > 400,000 km to the Moon. Our total displacement is now 800,000 km.
> > >
> > > Ok, so the displacement we have to calculate is one quarter of 800,000 km,
> > > or
> > > 200,000 km (there’s a reason why I picked 400,000 km...) So s = 2 x 10^8
> > > m.
> > >
> > > We simplify where possible, and set u to zero. As will be seen later, actual
> > > values of u won’t make much difference.
> > >
> > > So... 2 x 10^8 = 0 + 0.5at^2. Cool. at^2 = 4 x 10^8.
> > >
> > > Now, a =10. (keep things simple...) which means that
> > >
> > > 10t^2 = 4 x 10^8
> > >
> > > so... t^2 = 4 x 10 ^7.
> > >
> > > hmm. My calculator says that t must equal 6325 seconds, (105.4 minutes, 1.76
> > > hours) approximately. Hmm, We must do this four times (once accel going to
> > > the Moon, once delec to zero, once accel going back to Earth, once decel to
> > > zero) so that’s 25300 seconds, approximately.
> > >
> > > hmm. v = u + at. u = 0. v = at. a =10, t = 25300. So... your total mission
> > > delta vee is... 253,000 metres per second, 253 km/s. So... how much reaction
> > > mass are you going to need? delta-vee = ve x ln mr. The best chemical
> > > rockets
> > > have a ve on the order of 4 km/s. The natural log of the mass ratio is going
> > > to be... 63.25. You’re gonna need a who lot of go-juice. And now you know
> > > why NASA didn’t try to use continuous accel in the Apollo moonships.
> > > Either
> > > you’re going to need something hotter than a chemical rocket, or you
> > > can’t accel all the way. Hot-jet nukes might, in theory, get to 100 km/s
> > > ve... that at least gives a managable mr. Still not good, though. You need
> > > better. Fusion rockets would be a lot better. Photon rockets would be nice.
> > > Neither one is likely to be available for the near future, if at all.
> > > You’re gonna need to think carefully about what kind of trajectories you
> > > want to use, continuous accel is off the table. It’d be nice; 3.5 hours to
> > > the Moon, 7 hours for a round trip, a few days to Mars, a few weeks, at
> > > most,
> > > for anywhere in the system... Not happening without magic tech.
> > >
> > > Jerry Pournelle went into great detail about this kind of thing in his A
> > > Step
> > > Further Out columns in Galaxy, some of which were collected into a nice big
> > > paperback. Look it up.
> > > > Here's the weird thing. Regular
> > > > terrestrial cars can accelerate 0-60
> > > that’s miles per hour. Call it 100 km per hour. It’s 400,000 km to the
> > > Moon. That’s 4000 hours, assuming that the car could achieve escape
> > > velocity, which it can’t. (it’s worse than that, you have to flip and
> > > decel, so it’s gonna take longer)
> > > > in 10 seconds without even being
> > > > considered that fast, which comes out at 1 mile per second
> > > one mile per minute. 3600 mph is one mile per second. An SR-71 spy plane
> > > could hit 2000 to 2400 mph before atmospheric friction would heat it up and
> > > destroy it.
> > > > . That means if all
> > > > conventional limitations were removed (friction, cooling, controllability,
> > > > fuel supply, etc), the car could accelerate to 86,400 mph in 24 hours
> > > nope.
> > > > . The
> > > > monkey wrench is, 1 G of acceleration amounts to a change of only 35 kph or
> > > > 21 miles per hour,
> > > no. 1 gee is 10 m/s/s (approximately). That’s 10 metres per second per
> > > second. At the end of the first second, that’s 10 metres per second, 36000
> > > metres per hour, a.k.a. 360 km/s. At the end of the second second, that’s
> > > 20 m/s. At the end of the third, 30 m/s. Ten seconds in, 100 m/s.
> > > > and people aren't supposed to be able survive 10 G of
> > > > acceleration for more than a few seconds.
> > > it ain’t the people you should be concerned about, it’s the structure of
> > > your vehicle. Very few vehicles can take 10 gees.
> > > > Therefore, a manned vehicle
> > > > accelerating at +5040 miles per hour every 24 hours would already kill the
> > > > crew many times over. What am I missing here???
> > > yes. You accel at, say, 1 gee, and you get to anywhere in the system in
> > > under
> > > a month and a half. One gee. You’re mixing up velocity and acceleration.
> > >
> > > May I suggest a basic course on statics and dynamics?
> > > >
> > > >
> > > > David N. Brown
> > > > Mesa, Arizona
> > I have ridiculously detailed and probably incoherent specs for the ship in
> > chapters posted on my blog. It's called the Janus, and my head description is
> > Tinker Toy ship. My specs have been 360 m long (cut down from my very first
> > ideas) and 40-60 meters wide at one or two places including a Von Braun style
> > ring for artificial gravity. There's also supposed to be a fusion reactor and
> > a space shuttle-sized landing craft up front. The general idea was always
> > something long and skinny that could be simply lined with fuel. After putting
> > things down and getting feedback here, I recalculated the speed as 400,000
> > kph, to be reached with acceleration of +800 kph per hour. I now believe the
> > G count would come out as something like 0.022, which would be completely
> > pitiful for anything that wasn't in the size range of the Empire State
> > Building. It really would be a "different" approach to spaceship design.. It
> > could be called the Space Yugo, except the timeline would diverge before
> > communist Yugoslavia existed. Hope this makes a little more sense; I might
> > put up a link or so tomorrow.
> You still have a problem with ‘acceleration’ and ‘velocity’. I
> suspect that you’re making the Star Trek/Wars Error and have the decks
> parallel to the thrust. Won’t work. When under accel, down is aft.. When
> spinning, down is out. Spinning while under accel is a Bad Idea(™), as it
> will tend to induce nausea.
>
> So... here’s my first cut at Ship Fit To Rule The System: Manifest Destiny.
> ‘Cause the manifest destiny of anyone who gets in Manny Dee’s way is to
> become plasma.
>
> Manny Dee masses 500,000 tonnes, with crew, supplies, ammunition, etc., but
> no reaction mass for her main motors. She normally carries another 500,000
> tonnes of reaction mass: water. No, I don’t ship water up from Earth,
> there’s lots of water in comets, various asteroids, Saturn’s rings, and
> assorted other objects in Jupiter and Saturn orbit. This gives her a mass
> ratio of 2, and the natural log og 2 is 0.6931. Manny Dee has four main
> motors, with an exhaust velocity of 100,000 km/s (one third of lightspeed)
> ‘cause they’re really great fusion rocket thingies with lots of
> handwavium tech. And that number is easy to work with. Hmm. Manny Dee has a
> mission delta vee of 69,300 or so km/s. She can go anywhere in the solar
> system and get back on one tank of reaction mass.
>

William Hyde <wthyde1953@gmail.com> writes:
>On Wednesday, November 9, 2022 at 6:16:40 PM UTC-5, peterwezeman@hotmail.com wrote:
>> On Wednesday, November 9, 2022 at 2:22:01 PM UTC-6, David Brown wrote:
>
>> I have found _Physics: volume 1_ by Robert Resnick, David Halliday, and Kenneth Krane to be useful. The first
>> chapter is a good introduction to dimensions. Chapter 2 covers motion with constant acceleration.
>
>I second that. It's a very good high school text. Some universities used to use it as a first year text.

Wiley wants USD203.95 for it. Sigh.

On 10 Nov 2022, peterwezeman@hotmail.com wrote
(in article<aa4a4b63-9d37-465c-8a9b-5202f9f6fb44n@googlegroups.com>):

> On Thursday, November 10, 2022 at 8:38:11 AM UTC-6, Wolffan wrote:
> > On 10 Nov 2022, David Brown wrote
> > (in article<657e2ac8-4184-43f2...@googlegroups.com>):
> > > On Wednesday, November 9, 2022 at 4:21:59 PM UTC-7, Wolffan wrote:
> > > > On 09 Nov 2022, David Brown wrote
> > > > (in article<d672798f-3b06-4d93...@googlegroups.com>):
> > > > > Here's something I've been working on for a retro future project with
> > > > > hard
> > > > > sci fi elements. It calls for a gigantic 300+ meter ship
> > > > that’s aircraft carrier size. I hope that you’re starting from orbit,
> > > > or
> > > > there’s likely to be a problem.
> > > >
> > > > Also, that’s one dimension. What shape is it? It’s one thing if
> > > > it’s a
> > > > 300 metre long cylinder, with a diameter of, oh, 30 metres. It’s
> > > > something
> > > > else if it’s a 30-metre thick disk with a diameter of 300 metres.
> > > > It’s a
> > > > whole other thing if it’s a 300-metre radius sphere.
> > > > > to accelerate to
> > > > > 250,000 miles
> > > > 250,000 miles per what?
> > > > > for a trip to the outer solar system, which I arm waved to
> > > > > maybe +12,000 miles of acceleration per day.
> > > > you don’t do acceleration in miles per day. Personally, I work best in
> > > > SI
> > > > units: metres, kilogrammes, seconds, joules, watts, newtons, that kind of
> > > > thing. The acceleration due to gravity, one gee, is approximately 9.81
> > > > metres
> > > > per second per second. (that last ‘per second’ is kind of important)
> > > > One
> > > > gee is a rather significant acceleration. I usually just round up to a
> > > > nice
> > > > even 10 m/s/s, it’s easier to work with.
> > > >
> > > > Some basic concepts:
> > > >
> > > > delta-vee is the total mission change in velocity. It’s rather
> > > > significant.
> > > >
> > > > the mission delta-vee for a rocket-propelled vehicle is equal to the
> > > > rocket's
> > > > exhaust velocity times the natural log of the mass ratio, where the mass
> > > > ratio is the total mass of rocket, payload, reaction mass, and everything
> > > > else at the start of the flight (m1) divided my the mass of whatever is
> > > > left
> > > > at the end of the flight (m2). Note that that’s for the _total_ mission,
> > > > you usually need to get there and back.
> > > >
> > > > v = u + at. That is, the final velocity equals the intial velocity plus
> > > > the
> > > > acceleration times the time spent under acceleration.
> > > >
> > > > s = ut + 0.5at^2. That is, the displacement equals the inital velocity
> > > > times
> > > > the time under acceleration plus half the acceleration times the square of
> > > > the time.
> > > >
> > > > So let’s do an example: we want to go to the Moon. We want to do it at
> > > > one
> > > > gee continuous accel. We want to get back.
> > > >
> > > > So... the distance from the Earth to the Moon is 380,000 kilomtres, or 380
> > > > million mtres. That’s 3.8 x 10^8 metres. We have to get there and back.
> > > > That’s 7.6 x 10^8 metres. (It’s not really 380 million metres. See
> > > > below)
> > > >
> > > > Ok... problem. We need to arrive at the Moon with velocity of zero
> > > > relative
> > > > to the Moon. We need to get back to Earth, or at least Earth orbit, with
> > > > velocity zero. (well, we have to make lunar orbit and Earth orbit, but we
> > > > can
> > > > worry about that later.) This means that we can’t just boost all the
> > > > way,
> > > > we must boost half way, turn around, slow down. We must do this twice to
> > > > make
> > > > the round trip. As we need to fiddle around a little, let’s say that
> > > > it’s
> > > > 400,000 km to the Moon. Our total displacement is now 800,000 km.
> > > >
> > > > Ok, so the displacement we have to calculate is one quarter of 800,000 km,
> > > > or
> > > > 200,000 km (there’s a reason why I picked 400,000 km...) So s = 2 x 10^8
> > > > m.
> > > >
> > > > We simplify where possible, and set u to zero. As will be seen later,
> > > > actual
> > > > values of u won’t make much difference.
> > > >
> > > > So... 2 x 10^8 = 0 + 0.5at^2. Cool. at^2 = 4 x 10^8.
> > > >
> > > > Now, a =10. (keep things simple...) which means that
> > > >
> > > > 10t^2 = 4 x 10^8
> > > >
> > > > so... t^2 = 4 x 10 ^7.
> > > >
> > > > hmm. My calculator says that t must equal 6325 seconds, (105.4 minutes,
> > > > 1.76
> > > > hours) approximately. Hmm, We must do this four times (once accel going to
> > > > the Moon, once delec to zero, once accel going back to Earth, once decel
> > > > to
> > > > zero) so that’s 25300 seconds, approximately.
> > > >
> > > > hmm. v = u + at. u = 0. v = at. a =10, t = 25300. So... your total mission
> > > > delta vee is... 253,000 metres per second, 253 km/s. So... how much
> > > > reaction
> > > > mass are you going to need? delta-vee = ve x ln mr. The best chemical
> > > > rockets
> > > > have a ve on the order of 4 km/s. The natural log of the mass ratio is
> > > > going
> > > > to be... 63.25. You’re gonna need a who lot of go-juice. And now you
> > > > know
> > > > why NASA didn’t try to use continuous accel in the Apollo moonships.
> > > > Either
> > > > you’re going to need something hotter than a chemical rocket, or you
> > > > can’t accel all the way. Hot-jet nukes might, in theory, get to 100 km/s
> > > > ve... that at least gives a managable mr. Still not good, though. You need
> > > > better. Fusion rockets would be a lot better. Photon rockets would be
> > > > nice.
> > > > Neither one is likely to be available for the near future, if at all.
> > > > You’re gonna need to think carefully about what kind of trajectories you
> > > > want to use, continuous accel is off the table. It’d be nice; 3.5 hours
> > > > to
> > > > the Moon, 7 hours for a round trip, a few days to Mars, a few weeks, at
> > > > most,
> > > > for anywhere in the system... Not happening without magic tech.
> > > >
> > > > Jerry Pournelle went into great detail about this kind of thing in his A
> > > > Step
> > > > Further Out columns in Galaxy, some of which were collected into a nice
> > > > big
> > > > paperback. Look it up.
> > > > > Here's the weird thing. Regular
> > > > > terrestrial cars can accelerate 0-60
> > > > that’s miles per hour. Call it 100 km per hour. It’s 400,000 km to the
> > > > Moon. That’s 4000 hours, assuming that the car could achieve escape
> > > > velocity, which it can’t. (it’s worse than that, you have to flip and
> > > > decel, so it’s gonna take longer)
> > > > > in 10 seconds without even being
> > > > > considered that fast, which comes out at 1 mile per second
> > > > one mile per minute. 3600 mph is one mile per second. An SR-71 spy plane
> > > > could hit 2000 to 2400 mph before atmospheric friction would heat it up
> > > > and
> > > > destroy it.
> > > > > . That means if all
> > > > > conventional limitations were removed (friction, cooling,
> > > > > controllability,
> > > > > fuel supply, etc), the car could accelerate to 86,400 mph in 24 hours
> > > > nope.
> > > > > . The
> > > > > monkey wrench is, 1 G of acceleration amounts to a change of only 35 kph
> > > > > or
> > > > > 21 miles per hour,
> > > > no. 1 gee is 10 m/s/s (approximately). That’s 10 metres per second per
> > > > second. At the end of the first second, that’s 10 metres per second,
> > > > 36000
> > > > metres per hour, a.k.a. 360 km/s. At the end of the second second,
> > > > that’s
> > > > 20 m/s. At the end of the third, 30 m/s. Ten seconds in, 100 m/s.
> > > > > and people aren't supposed to be able survive 10 G of
> > > > > acceleration for more than a few seconds.
> > > > it ain’t the people you should be concerned about, it’s the structure
> > > > of
> > > > your vehicle. Very few vehicles can take 10 gees.
> > > > > Therefore, a manned vehicle
> > > > > accelerating at +5040 miles per hour every 24 hours would already kill
> > > > > the
> > > > > crew many times over. What am I missing here???
> > > > yes. You accel at, say, 1 gee, and you get to anywhere in the system in
> > > > under
> > > > a month and a half. One gee. You’re mixing up velocity and acceleration.
> > > >
> > > > May I suggest a basic course on statics and dynamics?
> > > > >
> > > > >
> > > > > David N. Brown
> > > > > Mesa, Arizona
> > > I have ridiculously detailed and probably incoherent specs for the ship in
> > > chapters posted on my blog. It's called the Janus, and my head description
> > > is
> > > Tinker Toy ship. My specs have been 360 m long (cut down from my very first
> > > ideas) and 40-60 meters wide at one or two places including a Von Braun
> > > style
> > > ring for artificial gravity. There's also supposed to be a fusion reactor
> > > and
> > > a space shuttle-sized landing craft up front. The general idea was always
> > > something long and skinny that could be simply lined with fuel. After
> > > putting
> > > things down and getting feedback here, I recalculated the speed as 400,000
> > > kph, to be reached with acceleration of +800 kph per hour. I now believe
> > > the
> > > G count would come out as something like 0.022, which would be completely
> > > pitiful for anything that wasn't in the size range of the Empire State
> > > Building. It really would be a "different" approach to spaceship design. It
> > > could be called the Space Yugo, except the timeline would diverge before
> > > communist Yugoslavia existed. Hope this makes a little more sense; I might
> > > put up a link or so tomorrow.
> > You still have a problem with ‘acceleration’ and ‘velocity’. I
> > suspect that you’re making the Star Trek/Wars Error and have the decks
> > parallel to the thrust. Won’t work. When under accel, down is aft. When
> > spinning, down is out. Spinning while under accel is a Bad Idea(™), as it
> > will tend to induce nausea.
> >
> > So... here’s my first cut at Ship Fit To Rule The System: Manifest
> > Destiny.
> > ‘Cause the manifest destiny of anyone who gets in Manny Dee’s way is to
> > become plasma.
> >
> > Manny Dee masses 500,000 tonnes, with crew, supplies, ammunition, etc., but
> > no reaction mass for her main motors. She normally carries another 500,000
> > tonnes of reaction mass: water. No, I don’t ship water up from Earth,
> > there’s lots of water in comets, various asteroids, Saturn’s rings, and
> > assorted other objects in Jupiter and Saturn orbit. This gives her a mass
> > ratio of 2, and the natural log og 2 is 0.6931. Manny Dee has four main
> > motors, with an exhaust velocity of 100,000 km/s (one third of lightspeed)
> > ‘cause they’re really great fusion rocket thingies with lots of
> > handwavium tech. And that number is easy to work with. Hmm. Manny Dee has a
> > mission delta vee of 69,300 or so km/s. She can go anywhere in the solar
> > system and get back on one tank of reaction mass.
>
> What nuclear reaction are you assuming to get an exhaust velocity
> of 100,000,000 meters per second (1/3 C) for a fusion rocket?

scott@slp53.sl.home (Scott Lurndal) wrote in
news:FTdbL.84233$2Rs3.64162@fx12.iad:

> William Hyde <wthyde1953@gmail.com> writes:
>>On Wednesday, November 9, 2022 at 6:16:40 PM UTC-5,
>>peterwezeman@hotmail.com wrote:
>>> On Wednesday, November 9, 2022 at 2:22:01 PM UTC-6, David
>>> Brown wrote:
>>
>>> I have found _Physics: volume 1_ by Robert Resnick, David
>>> Halliday, and Kenneth Krane to be useful. The first chapter is
>>> a good introduction to dimensions. Chapter 2 covers motion
>>> with constant acceleration.
>>
>>I second that. It's a very good high school text. Some
>>universities used to use it as a first year text.
>
> Wiley wants USD203.95 for it. Sigh.
>
Amazon has it (used) for less than $40.

--
Terry Austin

"Terry Austin: like the polio vaccine, only with more asshole."
-- David Bilek

Jesus forgives sinners, not criminals.

Jibini Kula Tumbili Kujisalimisha <taustinca@gmail.com> writes:
>scott@slp53.sl.home (Scott Lurndal) wrote in
>news:FTdbL.84233$2Rs3.64162@fx12.iad:
>
>> William Hyde <wthyde1953@gmail.com> writes:
>>>On Wednesday, November 9, 2022 at 6:16:40 PM UTC-5,
>>>peterwezeman@hotmail.com wrote:
>>>> On Wednesday, November 9, 2022 at 2:22:01 PM UTC-6, David
>>>> Brown wrote:
>>>
>>>> I have found _Physics: volume 1_ by Robert Resnick, David
>>>> Halliday, and Kenneth Krane to be useful. The first chapter is
>>>> a good introduction to dimensions. Chapter 2 covers motion
>>>> with constant acceleration.
>>>
>>>I second that. It's a very good high school text. Some
>>>universities used to use it as a first year text.
>>
>> Wiley wants USD203.95 for it. Sigh.
>>
>Amazon has it (used) for less than $40.
>

The ones for less than $40 on Amazon that I saw were all
rentals. For two months.

On Thursday, November 10, 2022 at 5:01:42 PM UTC-5, Scott Lurndal wrote:
> Jibini Kula Tumbili Kujisalimisha <taus...@gmail.com> writes:
> >sc...@slp53.sl.home (Scott Lurndal) wrote in
> >news:FTdbL.84233$2Rs3....@fx12.iad:
> >
> >> William Hyde <wthyd...@gmail.com> writes:
> >>>On Wednesday, November 9, 2022 at 6:16:40 PM UTC-5,
> >>>peterw...@hotmail.com wrote:
> >>>> On Wednesday, November 9, 2022 at 2:22:01 PM UTC-6, David
> >>>> Brown wrote:
> >>>
> >>>> I have found _Physics: volume 1_ by Robert Resnick, David
> >>>> Halliday, and Kenneth Krane to be useful. The first chapter is
> >>>> a good introduction to dimensions. Chapter 2 covers motion
> >>>> with constant acceleration.
> >>>
> >>>I second that. It's a very good high school text. Some
> >>>universities used to use it as a first year text.
> >>
> >> Wiley wants USD203.95 for it. Sigh.
> >>
> >Amazon has it (used) for less than $40.
> >
> The ones for less than $40 on Amazon that I saw were all
> rentals. For two months.

A softcover of chapters 1-12 is about five dollars at abe books.

William Hyde

On Thursday, 10 November 2022 at 19:24:51 UTC, Scott Lurndal wrote:
> David Brown <davidn...@gmail.com> writes:
> >On Thursday, November 10, 2022 at 7:31:10 AM UTC-7, Scott Lurndal wrote:
> >> David Brown <davidn...@gmail.com> writes:=20
> >> >On Wednesday, November 9, 2022 at 4:21:59 PM UTC-7, Wolffan wrote:
> >> <snip long physics lesson>
> >> >> > crew many times over. What am I missing here???
> >> >> yes. You accel at, say, 1 gee, and you get to anywhere in the system i=
> >n u=3D=20
> >> >nder=3D20=20
> >> >> a month and a half. One gee. You=3DE2=3D80=3D99re mixing up velocity a=
> >nd accele=3D=20
> >> >ration.=3D20=20
> >> >>=3D20
> >> >> May I suggest a basic course on statics and dynamics?
> >> >> >=3D20=20
> >> >> >=3D20=20
> >> >> > David N. Brown=3D20=20
> >> >> > Mesa, Arizona=20
> >> >I have ridiculously detailed and probably incoherent specs for the ship =
> >in =3D=20
> >> >chapters posted on my blog. It's called the Janus, and my head descripti=
> >on =3D=20
> >> >is Tinker Toy ship. My specs have been 360 m long (cut down from my very=
> > fi=3D=20
> >> >rst ideas) and 40-60 meters wide at one or two places including a Von Br=
> >aun=3D
> >> > style ring for artificial gravity.
> >> So many 'spaceship' designs follow terrestrial characteristics (i.e. typi=
> >cally=20
> >> cylindrical, or in the case of Star Wars, et. al., space-born aircraft ca=
> >rriers).=20
> >>=20
> >> For spaceships that never intend to fly -in- atmosphere, it would seem th=
> >at the sphere=20
> >> is the optimal form factor (given structural loading from internal atomsp=
> >heric pressure),=20
> >> and the movie form (e.g. star wars) would be far from optimal.=20
> >>=20
> >> The enterprise is pretty, but not particularly optimal, particularly the=
> >=20
> >> saucer section.
> >I've been a defender of the old-fashioned flying saucer, at least in its tr=
> >uly radial variations. It lets you keep the command center and vital system=
> >s in a small area, while still allowing you to spread the engines, sensors =
> >and weapons (if any) across a 360 arc. Also, if there's incoming debris or =
> >actual weapons fire, there's still one axis that's mostly flat. Ironically,=
> > the Millennium Falcon is the one cinematic ship to be shown taking advanta=
> >ge of these characteristics, and it still had some terrible design features=
> > (partly because the life-sized sets had been created for a completely diff=
> >erent ship).
>
> Your typical tube airliner (e.g. 737) has an internal pressure of 11psi
> at a cruising altitude of 35,000 feet where the external pressure is
> less than 4psi. That's over 7 pounds per square inch of pressure
> on the internal cabin area
> that needs to be designed for; the rear bulkhead, for instance is
> dome shaped, rather than flat.
>
>
> https://aviation.stackexchange.com/questions/31292/why-do-airliners-have-pressure-bulkheads
>
> "The shape of the final aft section is not well suited to resist
> pressurization stresses: the best shape is a sphere; the cylinder
> (with spherical terminations) comes a close second. The conical
> shape would require serious stiffeners to survive pressurization
> cycles for the whole life of the aircraft; the bulkhead solves
> this problem by using a shape that is naturally more resistant
> to stresses - and thus can be built with less material - leading
> to less weight, and hence fuel savings (in addition to the increased safety)."
>
> "It's worth making a rough estimate of just how big the force on
> such a bulkhead is. At sea level, atmospheric pressure of 14.7 psi
> is roughly the same as 1 ton per square foot. The difference between
> the internal and external pressure at cruising altitude is about half
> that value. The fuselage diameter of a B777 is about 20 feet, so the
> area of the bulkhead is about 300 square feet. So the total force on
> the bulkhead is about 150 tons. Compare that with the max takeoff weight
> of the plane, which is about 250 tons - it's a seriously large number."
>
> While a ship designed to remain in space permenently won't be subjected
> to pressurization cycles, a spherical shape will continue to be
> optimal to deal with stresses.
>
> Question: What affect does acceleration have on the atmosphere within
> the spaceship?

Logically (after Einstein), it's the same as the effect of gravity.
Considered as a "traditional" rocket, air pressure is less at the
"top" end than at the bottom. !I mean, if your spaceship is
big enough for this to be inconvenient, then you have decks
pressurized independently.

Sometimes I feel my ears under strain in the elevator ride
at work of a dozen floors or so, and while acceleration
occurs, I think gravity is mainly to blame.

The elevators are odd: for promotion reasons, I suspect,
the "which floor are you at" indicator sign reaches your
destination an absurdly long time before you do.

Or maybe it's something about relativity that I haven't
considered.

On 11/10/2022 10:07 AM, rkshullat@rosettacondot.com wrote:
> peterwezeman@hotmail.com <peterwezeman@hotmail.com> wrote:
>> On Wednesday, November 9, 2022 at 2:22:01 PM UTC-6, David Brown wrote:
>>> On Wednesday, November 9, 2022 at 9:41:50 AM UTC-7, Michael F. Stemper wrote:
>>>> On 09/11/2022 10.21, David Brown wrote:
>>>>> Here's something I've been working on for a retro future project with hard sci fi elements. It calls for a gigantic 300+ meter ship to accelerate to 250,000 miles for a trip to the outer solar system, which I arm waved to maybe +12,000 miles of acceleration per day. Here's the weird thing. Regular terrestrial cars can accelerate 0-60 in 10 seconds without even being considered that fast, which comes out at 1 mile per second. That means if all conventional limitations were removed (friction, cooling, controllability, fuel supply, etc), the car could accelerate to 86,400 mph in 24 hours. The monkey wrench is, 1 G of acceleration amounts to a change of only 35 kph or 21 miles per hour, and people aren't supposed to be able survive 10 G of acceleration for more than a few seconds. Therefore, a manned vehicle accelerating at +5040 miles per hour every 24 hours would already kill the crew many times over. What am I missing here???
>>>> If you're going to try to do hard science, you need to start by understanding
>>>> units of measure. One accelerates to a velocity (speed). You have your ship
>>>> accelerating to a distance -- 250000 miles. That means that after it has gone
>>>> that far it stops accelerating.
>>>>
>>>> I think that you probably want it to accelerate up to some speed, such as:
>>>> - 250000 miles/year
>>>> - 250000 miles/month
>>>> - 250000 miles/day
>>>> - 250000 miles/hour
>>>> Something like one of those.
>>>>
>>>> For instance, let's take a look at your car example. When you discuss a car
>>>> accelerating from 0-60, it means from 0 miles per hour to 60 miles per hour,
>>>> two speeds. That change in speed, if spread out evenly over a ten-second
>>>> interval, would not be one mile per second (as you stated), but six miles per
>>>> hour per second.
>>>>
>>>> I think that you need to sit down with pencil and paper and work through all
>>>> of this, making the units explicit throughout your work.
>>>>
>>>> Getting to your last question, the units are correct here (although I have
>>>> no idea whether it's consistent with anything that went before).
>>>>
>>>> 5040 miles per hour per day works out to 210 miles per hour per hour, which
>>>> means that over a period of one hour, you've sped up by 210 miles per hour.
>>>> If you think about it, a commercial airliner speeds up from stopped on the
>>>> tarmac to a speed speed of over 500 miles per hour in a matter of ten minutes
>>>> or so, which is an acceleration of about 3000 miles per hour per hour, or
>>>> much greater than what is mentioned here.
>>>>
>>>> By the way, this would be much less subject to error if you did your work
>>>> exclusively in meters and seconds.
>>>>
>>>> --
>>>> Michael F. Stemper
>>>> Economists have correctly predicted seven of the last three recessions.
>>> Thanks for this. For further context, my core parameters are a ship that could make a trip from Mars to Neptune in 20 months, assuming the former to be partly colonized by the late 20th/ early 21st century. Outside of some shorthand, I'd say this confirms my numbers are "realistic", to the extent they describe how manned vehicles behave. I would assume I'm missing something about how horizontal acceleration converts to normally vertical gravitational force, but I'm not sure what the details would be.
>>
>> I have found _Physics: volume 1_ by Robert Resnick, David Halliday, and Kenneth Krane to be useful. The first
>> chapter is a good introduction to dimensions. Chapter 2 covers motion with constant acceleration.
>>
>> One possible source of confusion is that horizontal speeds are often given in miles per hour or kilometers
>> hour whereas accelerations are given in feet per second per second or meters per second per second.
>> As Michael Stemper suggests, try keeping the units consistent.
>
> When my wife and I were in college our physics professors put a lot of
> emphasis on dimensional analysis:
> <https://en.wikipedia.org/wiki/Dimensional_analysis>
> She's continued the tradition with her students.
> Getting the units right isn't a guarantee that you're correct but getting them
> wrong pretty much ensures that you're incorrect.
> My into physics professor loved to give problems in unusual units with the
> answer in a different set (start with meters and hours and calculate velocity
> in furlongs per fortnight). You learned very quickly to convert to consistent
> units and carry those all the way through.
>
> Robert

Keeping dimensional units correct is the hardest thing to do in our
software. The old portion of the software is lbmol, R, psia, feet, etc.
Other portions are kgmol or gmmol, K, kg/cm2 or pascal, meter, etc.
Things can get dicey in a hurry.

Lynn

On 11/9/2022 10:21 AM, David Brown wrote:
> Here's something I've been working on for a retro future project with hard sci fi elements. It calls for a gigantic 300+ meter ship to accelerate to 250,000 miles for a trip to the outer solar system, which I arm waved to maybe +12,000 miles of acceleration per day. Here's the weird thing. Regular terrestrial cars can accelerate 0-60 in 10 seconds without even being considered that fast, which comes out at 1 mile per second. That means if all conventional limitations were removed (friction, cooling, controllability, fuel supply, etc), the car could accelerate to 86,400 mph in 24 hours. The monkey wrench is, 1 G of acceleration amounts to a change of only 35 kph or 21 miles per hour, and people aren't supposed to be able survive 10 G of acceleration for more than a few seconds. Therefore, a manned vehicle accelerating at +5040 miles per hour every 24 hours would already kill the crew many times over. What am I missing here???
>
> David N. Brown
> Mesa, Arizona

John Varley wrote that any spaceship with a 1G engine can make it from
Earth to Mars in a week, including both acceleration and deceleration,
in his excellent "Red Thunder" book. I have not done the math though.
https://www.amazon.com/Red-Thunder-Lightning-Novel/dp/0441011624/

1G = 9.8 m/sec^2 = 32.2 feet/sec^2 = 78973 mile/hour^2

At the beginning, you are at rest. At 1g, you are at 78,793 miles/hour
in one hour. Mass is not a factor other than it determines the size of
the engine.

Lynn

On Thursday, November 10, 2022 at 6:35:42 AM UTC+11, peterwezeman@hotmail.com wrote:
> On Wednesday, November 9, 2022 at 10:41:50 AM UTC-6, Michael F. Stemper wrote:
> > On 09/11/2022 10.21, David Brown wrote:
> > > Here's something I've been working on for a retro future project with hard sci fi elements. It calls for a gigantic 300+ meter ship to accelerate to 250,000 miles for a trip to the outer solar system, which I arm waved to maybe +12,000 miles of acceleration per day. Here's the weird thing. Regular terrestrial cars can accelerate 0-60 in 10 seconds without even being considered that fast, which comes out at 1 mile per second. That means if all conventional limitations were removed (friction, cooling, controllability, fuel supply, etc), the car could accelerate to 86,400 mph in 24 hours. The monkey wrench is, 1 G of acceleration amounts to a change of only 35 kph or 21 miles per hour, and people aren't supposed to be able survive 10 G of acceleration for more than a few seconds. Therefore, a manned vehicle accelerating at +5040 miles per hour every 24 hours would already kill the crew many times over. What am I missing here???
> > If you're going to try to do hard science, you need to start by understanding
> > units of measure. One accelerates to a velocity (speed). You have your ship
> > accelerating to a distance -- 250000 miles. That means that after it has gone
> > that far it stops accelerating.
> >
> > I think that you probably want it to accelerate up to some speed, such as:
> > - 250000 miles/year
> > - 250000 miles/month
> > - 250000 miles/day
> > - 250000 miles/hour
> > Something like one of those.
> >
> > For instance, let's take a look at your car example. When you discuss a car
> > accelerating from 0-60, it means from 0 miles per hour to 60 miles per hour,
> > two speeds. That change in speed, if spread out evenly over a ten-second
> > interval, would not be one mile per second (as you stated), but six miles per
> > hour per second.
> >
> > I think that you need to sit down with pencil and paper and work through all
> > of this, making the units explicit throughout your work.
> >
> > Getting to your last question, the units are correct here (although I have
> > no idea whether it's consistent with anything that went before).
> >
> > 5040 miles per hour per day works out to 210 miles per hour per hour, which
> > means that over a period of one hour, you've sped up by 210 miles per hour.
> > If you think about it, a commercial airliner speeds up from stopped on the
> > tarmac to a speed speed of over 500 miles per hour in a matter of ten minutes
> > or so, which is an acceleration of about 3000 miles per hour per hour, or
> > much greater than what is mentioned here.
> >
> > By the way, this would be much less subject to error if you did your work
> > exclusively in meters and seconds.
> This reminds me of a story. Someone bought a high-performance Italian
> sports car, and was showing it to her friend, another enthusiast, for the
> first time. After riding as a passenger over some challenging roads it
> was his turn to drive. Taking the driver's seat, he listened attentively to
> her pointers. Before they started off she said, "And remember, the
> speedometer is calibrated in metric units."
>
> He let in the clutch and accelerated cautiously to 60, getting the feel of
> the car. After a short time he asked, "Have you checked the speedometer
> with a stopwatch? I've driven in Europe, and it sure seems to me that
> we're going faster than sixty kilometers per hour."
>
> She replied, "We are. That's meters per second."
>
60 kmph is 16.67 mps
60 mps is 216 kmph

I'll admit that a car can feel very different at speeds (I was badly fooled by a work car once) but that difference in speed should be readily apparent from visual cues

scott@slp53.sl.home (Scott Lurndal) wrote in
news:5xebL.6840$ITE9.5044@fx40.iad:

> Jibini Kula Tumbili Kujisalimisha <taustinca@gmail.com> writes:
>>scott@slp53.sl.home (Scott Lurndal) wrote in
>>news:FTdbL.84233$2Rs3.64162@fx12.iad:
>>
>>> William Hyde <wthyde1953@gmail.com> writes:
>>>>On Wednesday, November 9, 2022 at 6:16:40 PM UTC-5,
>>>>peterwezeman@hotmail.com wrote:
>>>>> On Wednesday, November 9, 2022 at 2:22:01 PM UTC-6, David
>>>>> Brown wrote:
>>>>
>>>>> I have found _Physics: volume 1_ by Robert Resnick, David
>>>>> Halliday, and Kenneth Krane to be useful. The first chapter
>>>>> is a good introduction to dimensions. Chapter 2 covers
>>>>> motion with constant acceleration.
>>>>
>>>>I second that. It's a very good high school text. Some
>>>>universities used to use it as a first year text.
>>>
>>> Wiley wants USD203.95 for it. Sigh.
>>>
>>Amazon has it (used) for less than $40.
>>
>
> The ones for less than $40 on Amazon that I saw were all
> rentals. For two months.

To to:

https://www.amazon.com/Physics-1-Robert-Resnick/dp/0471320579/ref=s
r_1_6?crid=28BL41HYHS8AW&keywords=robert+resnick&qid=1668141272&spr
efix=robert+resnick%2Caps%2C161&sr=8-6

https://tinyurl.com/56cwpptc

And follow the link to "46 Used from $32.43" under the Hardcover
price.

(And for that matter, there's an option on that page to buy used
for $44.23)

--
Terry Austin

Proof that Alan Baker is a liar and a fool, and even stupider than
Lynn: https://www.cbp.gov/newsroom/stats/sw-border-migration

"Terry Austin: like the polio vaccine, only with more asshole."
-- David Bilek

Jesus forgives sinners, not criminals.

On 10/11/2022 18.12, Lynn McGuire wrote:
> On 11/10/2022 10:07 AM, rkshullat@rosettacondot.com wrote:
>> peterwezeman@hotmail.com <peterwezeman@hotmail.com> wrote:

>>> One possible source of confusion is that horizontal speeds are often given in miles per hour or kilometers
>>> hour whereas accelerations are given in feet per second per second or meters per second per second.
>>> As Michael Stemper suggests, try keeping the units consistent.
>>
>> When my wife and I were in college our physics professors put a lot of
>> emphasis on dimensional analysis:
>> <https://en.wikipedia.org/wiki/Dimensional_analysis>
>> She's continued the tradition with her students.
>> Getting the units right isn't a guarantee that you're correct but getting them
>> wrong pretty much ensures that you're incorrect.
>> My into physics professor loved to give problems in unusual units with the
>> answer in a different set (start with meters and hours and calculate velocity
>> in furlongs per fortnight). You learned very quickly to convert to consistent
>> units and carry those all the way through.

> Keeping dimensional units correct is the hardest thing to do in our software.  The old portion of the software is lbmol, R, psia, feet, etc.  Other portions are kgmol or gmmol, K, kg/cm2 or pascal, meter, etc. Things can get dicey in a hurry.

I know that you have a large existing code base in FORTRAN. However,
you might be interested (for future development) in this python module,
which does arithmetic on dimensioned quantities:
<https://pypi.org/project/units/>

It supports standard units, as well as allowing you to roll your own.

Headline:

Provides support for quantities and units, which strictly disallow invalid
operations between incompatible quantities. For example, we cannot add 2 metres
to 5 seconds, because this doesn’t make sense.

--
Michael F. Stemper
Psalm 82:3-4

Lynn McGuire <lynnmcguire5@gmail.com> wrote:
> On 11/10/2022 10:07 AM, rkshullat@rosettacondot.com wrote:
>> peterwezeman@hotmail.com <peterwezeman@hotmail.com> wrote:
>>> On Wednesday, November 9, 2022 at 2:22:01 PM UTC-6, David Brown wrote:
>>>> On Wednesday, November 9, 2022 at 9:41:50 AM UTC-7, Michael F. Stemper wrote:
>>>>> On 09/11/2022 10.21, David Brown wrote:
>>>>>> Here's something I've been working on for a retro future project with hard sci fi elements. It calls for a gigantic 300+ meter ship to accelerate to 250,000 miles for a trip to the outer solar system, which I arm waved to maybe +12,000 miles of acceleration per day. Here's the weird thing. Regular terrestrial cars can accelerate 0-60 in 10 seconds without even being considered that fast, which comes out at 1 mile per second. That means if all conventional limitations were removed (friction, cooling, controllability, fuel supply, etc), the car could accelerate to 86,400 mph in 24 hours. The monkey wrench is, 1 G of acceleration amounts to a change of only 35 kph or 21 miles per hour, and people aren't supposed to be able survive 10 G of acceleration for more than a few seconds. Therefore, a manned vehicle accelerating at +5040 miles per hour every 24 hours would already kill the crew many times over. What am I missing here???
>>>>> If you're going to try to do hard science, you need to start by understanding
>>>>> units of measure. One accelerates to a velocity (speed). You have your ship
>>>>> accelerating to a distance -- 250000 miles. That means that after it has gone
>>>>> that far it stops accelerating.
>>>>>
>>>>> I think that you probably want it to accelerate up to some speed, such as:
>>>>> - 250000 miles/year
>>>>> - 250000 miles/month
>>>>> - 250000 miles/day
>>>>> - 250000 miles/hour
>>>>> Something like one of those.
>>>>>
>>>>> For instance, let's take a look at your car example. When you discuss a car
>>>>> accelerating from 0-60, it means from 0 miles per hour to 60 miles per hour,
>>>>> two speeds. That change in speed, if spread out evenly over a ten-second
>>>>> interval, would not be one mile per second (as you stated), but six miles per
>>>>> hour per second.
>>>>>
>>>>> I think that you need to sit down with pencil and paper and work through all
>>>>> of this, making the units explicit throughout your work.
>>>>>
>>>>> Getting to your last question, the units are correct here (although I have
>>>>> no idea whether it's consistent with anything that went before).
>>>>>
>>>>> 5040 miles per hour per day works out to 210 miles per hour per hour, which
>>>>> means that over a period of one hour, you've sped up by 210 miles per hour.
>>>>> If you think about it, a commercial airliner speeds up from stopped on the
>>>>> tarmac to a speed speed of over 500 miles per hour in a matter of ten minutes
>>>>> or so, which is an acceleration of about 3000 miles per hour per hour, or
>>>>> much greater than what is mentioned here.
>>>>>
>>>>> By the way, this would be much less subject to error if you did your work
>>>>> exclusively in meters and seconds.
>>>>>
>>>>> --
>>>>> Michael F. Stemper
>>>>> Economists have correctly predicted seven of the last three recessions.
>>>> Thanks for this. For further context, my core parameters are a ship that could make a trip from Mars to Neptune in 20 months, assuming the former to be partly colonized by the late 20th/ early 21st century. Outside of some shorthand, I'd say this confirms my numbers are "realistic", to the extent they describe how manned vehicles behave. I would assume I'm missing something about how horizontal acceleration converts to normally vertical gravitational force, but I'm not sure what the details would be.
>>>
>>> I have found _Physics: volume 1_ by Robert Resnick, David Halliday, and Kenneth Krane to be useful. The first
>>> chapter is a good introduction to dimensions. Chapter 2 covers motion with constant acceleration.
>>>
>>> One possible source of confusion is that horizontal speeds are often given in miles per hour or kilometers
>>> hour whereas accelerations are given in feet per second per second or meters per second per second.
>>> As Michael Stemper suggests, try keeping the units consistent.
>>
>> When my wife and I were in college our physics professors put a lot of
>> emphasis on dimensional analysis:
>> <https://en.wikipedia.org/wiki/Dimensional_analysis>
>> She's continued the tradition with her students.
>> Getting the units right isn't a guarantee that you're correct but getting them
>> wrong pretty much ensures that you're incorrect.
>> My into physics professor loved to give problems in unusual units with the
>> answer in a different set (start with meters and hours and calculate velocity
>> in furlongs per fortnight). You learned very quickly to convert to consistent
>> units and carry those all the way through.
>>
>> Robert
>
> Keeping dimensional units correct is the hardest thing to do in our
> software. The old portion of the software is lbmol, R, psia, feet, etc.
> Other portions are kgmol or gmmol, K, kg/cm2 or pascal, meter, etc.
> Things can get dicey in a hurry.

She and I both majored in astrophysics, so we got used to it fast. Physics
classes used SI units and astronomy/astrophysics used cgs, although I see that
the IAU officially changed to SI in 1989 (we predate that).
Some of my wife's students have struggled not only with the concept that
fundamental physical constants have units but that the units themselves are
frequently derived quantities. We tend to think of volts as, well, volts.

Robert
--
Robert K. Shull Email: rkshull at rosettacon dot com

rkshullat@rosettacondot.com on Fri, 11 Nov 2022 14:28:43 -0000 (UTC)
typed in rec.arts.sf.written the following:
>
>>> Getting the units right isn't a guarantee that you're correct but getting them
>>> wrong pretty much ensures that you're incorrect.
>>> My into physics professor loved to give problems in unusual units with the
>>> answer in a different set (start with meters and hours and calculate velocity
>>> in furlongs per fortnight). You learned very quickly to convert to consistent
>>> units and carry those all the way through.
>>>
>>> Robert
>>
>> Keeping dimensional units correct is the hardest thing to do in our
>> software. The old portion of the software is lbmol, R, psia, feet, etc.
>> Other portions are kgmol or gmmol, K, kg/cm2 or pascal, meter, etc.
>> Things can get dicey in a hurry.
>
>She and I both majored in astrophysics, so we got used to it fast. Physics
>classes used SI units and astronomy/astrophysics used cgs, although I see that
>the IAU officially changed to SI in 1989 (we predate that).
>Some of my wife's students have struggled not only with the concept that
>fundamental physical constants have units but that the units themselves are
>frequently derived quantities. We tend to think of volts as, well, volts.

One element of switching to SI units: ease of mental calculations.
E.g., I can "estimate" G at 10 m/s which simplifies the estimations.
Meter to Kilometers to Light years "in round numbers" is 3 times
86 is 256, times 365 is "too many digits" plus eight zeros is even
more too many digits, but umm okay, ..."a lot". "Trillions".

--
pyotr filipivich
This Week's Panel: Us & Them - Eliminating Them.
Next Month's Panel: Having eliminated the old Them(tm)
Selecting who insufficiently Woke(tm) as to serve as the new Them(tm)

scott@slp53.sl.home (Scott Lurndal) on Thu, 10 Nov 2022 19:24:46 GMT
typed in rec.arts.sf.written the following:
>
>While a ship designed to remain in space permenently won't be subjected
>to pressurization cycles, a spherical shape will continue to be
>optimal to deal with stresses.

A ship in space is not completely free of pressurization cycles.
Air locks for example. Atmospheric "sloshing" as it starts and stops
acceleration.
>
>Question: What affect does acceleration have on the atmosphere within
>the spaceship?

It piles up at the "bottom" (along with the dust). Which in a
small compartment may not be all that much floor to ceiling. But an
open corridor the length of a ship may get some serious differential.
Depends on A) ship's environmental pressure and B) acceleration.

Practical matters aside, how little acceleration do humans need to
"function". Somewhere less than the surface gravity of the moon is
what I think.
--
pyotr filipivich
This Week's Panel: Us & Them - Eliminating Them.
Next Month's Panel: Having eliminated the old Them(tm)
Selecting who insufficiently Woke(tm) as to serve as the new Them(tm)

In article <iftsmhtbf5n7t48omgtr2nkhfpo24k6a8u@4ax.com>,
pyotr filipivich <phamp@mindspring.com> wrote:
>
>Practical matters aside, how little acceleration do humans need to
>"function". Somewhere less than the surface gravity of the moon is
>what I think.

Based on what?

--
My reviews can be found at http://jamesdavisnicoll.com/
My tor pieces at https://www.tor.com/author/james-davis-nicoll/
My Dreamwidth at https://james-davis-nicoll.dreamwidth.org/
My patreon is at https://www.patreon.com/jamesdnicoll

On 11/11/2022 8:27 AM, pyotr filipivich wrote:
> scott@slp53.sl.home (Scott Lurndal) on Thu, 10 Nov 2022 19:24:46 GMT
> typed in rec.arts.sf.written the following:
>>
>> While a ship designed to remain in space permenently won't be subjected
>> to pressurization cycles, a spherical shape will continue to be
>> optimal to deal with stresses.
>
> A ship in space is not completely free of pressurization cycles.
> Air locks for example. Atmospheric "sloshing" as it starts and stops
> acceleration.
>>
>> Question: What affect does acceleration have on the atmosphere within
>> the spaceship?
>
> It piles up at the "bottom" (along with the dust). Which in a
> small compartment may not be all that much floor to ceiling. But an
> open corridor the length of a ship may get some serious differential.
> Depends on A) ship's environmental pressure and B) acceleration.
>
> Practical matters aside, how little acceleration do humans need to
> "function". Somewhere less than the surface gravity of the moon is
> what I think.

I think that last depends on your definition of "function" and for how
long. Just visit and work for a few days or weeks? Do yearly
rotations? Live there permanently?

We already know from experience with the ISS that a year or less in
micro-gravity can have permanent medical/health effects. I suspect that
the longer one expects humans to stay there the closer to 1G the
environment needs to be for them to remain "functional".

--
I've done good in this world. Now I'm tired and just want to be a cranky
dirty old man.

On Thu, 10 Nov 2022 11:47:30 -0800 (PST), William Hyde
<wthyde1953@gmail.com> wrote:

>On Wednesday, November 9, 2022 at 6:16:40 PM UTC-5, peterwezeman@hotmail.com wrote:
>> On Wednesday, November 9, 2022 at 2:22:01 PM UTC-6, David Brown wrote:
>
>> I have found _Physics: volume 1_ by Robert Resnick, David Halliday, and Kenneth Krane to be useful. The first
>> chapter is a good introduction to dimensions. Chapter 2 covers motion with constant acceleration.
>
>I second that. It's a very good high school text. Some universities used to use it as a first year text.

I still have Parts 1 & 2 in one volume. This is from the mid-80s or
before. This was an introductory course in a University.

If he can find it, it should be very helpful to the OP.
--
"In this connexion, unquestionably the most significant
development was the disintegration, under Christian
influence, of classical conceptions of the family and
of family right."

On Thu, 10 Nov 2022 22:01:37 GMT, scott@slp53.sl.home (Scott Lurndal)
wrote:

>Jibini Kula Tumbili Kujisalimisha <taustinca@gmail.com> writes:
>>scott@slp53.sl.home (Scott Lurndal) wrote in
>>news:FTdbL.84233$2Rs3.64162@fx12.iad:
>>
>>> William Hyde <wthyde1953@gmail.com> writes:
>>>>On Wednesday, November 9, 2022 at 6:16:40 PM UTC-5,
>>>>peterwezeman@hotmail.com wrote:
>>>>> On Wednesday, November 9, 2022 at 2:22:01 PM UTC-6, David
>>>>> Brown wrote:
>>>>
>>>>> I have found _Physics: volume 1_ by Robert Resnick, David
>>>>> Halliday, and Kenneth Krane to be useful. The first chapter is
>>>>> a good introduction to dimensions. Chapter 2 covers motion
>>>>> with constant acceleration.
>>>>
>>>>I second that. It's a very good high school text. Some
>>>>universities used to use it as a first year text.
>>>
>>> Wiley wants USD203.95 for it. Sigh.
>>>
>>Amazon has it (used) for less than $40.
>>
>
>The ones for less than $40 on Amazon that I saw were all
>rentals. For two months.

The rentals are up-front and obvious.

Purchases are further down on the page.

When I was at the University (both times), we bought the course
textbooks at the start of the quarter and (usually) sold them back at
the end of the quarter. So, in effect, we were renting textbooks even
then.

But those were three-month quarters. What's two months? A
half-semester?
--
"In this connexion, unquestionably the most significant
development was the disintegration, under Christian
influence, of classical conceptions of the family and
of family right."

On 11/11/2022 8:13 AM, Michael F. Stemper wrote:
> On 10/11/2022 18.12, Lynn McGuire wrote:
>> On 11/10/2022 10:07 AM, rkshullat@rosettacondot.com wrote:
>>> peterwezeman@hotmail.com <peterwezeman@hotmail.com> wrote:
>
>>>> One possible source of confusion is that horizontal speeds are often
>>>> given in miles per hour or kilometers
>>>> hour whereas accelerations are given in feet per second per second
>>>> or meters per second per second.
>>>> As Michael Stemper suggests, try keeping the units consistent.
>>>
>>> When my wife and I were in college our physics professors put a lot of
>>> emphasis on dimensional analysis:
>>> <https://en.wikipedia.org/wiki/Dimensional_analysis>
>>> She's continued the tradition with her students.
>>> Getting the units right isn't a guarantee that you're correct but
>>> getting them
>>> wrong pretty much ensures that you're incorrect.
>>> My into physics professor loved to give problems in unusual units
>>> with the
>>> answer in a different set (start with meters and hours and calculate
>>> velocity
>>> in furlongs per fortnight). You learned very quickly to convert to
>>> consistent
>>> units and carry those all the way through.
>
>> Keeping dimensional units correct is the hardest thing to do in our
>> software.  The old portion of the software is lbmol, R, psia, feet,
>> etc.  Other portions are kgmol or gmmol, K, kg/cm2 or pascal, meter,
>> etc. Things can get dicey in a hurry.
>
> I know that you have a large existing code base in FORTRAN. However,
> you might be interested (for future development) in this python module,
> which does arithmetic on dimensioned quantities:
> <https://pypi.org/project/units/>
>
> It supports standard units, as well as allowing you to roll your own.
>
> Headline:
>
>   Provides support for quantities and units, which strictly disallow
> invalid
>   operations between incompatible quantities. For example, we cannot
> add 2 metres
>   to 5 seconds, because this doesn’t make sense.

I am in the beginning of converting my 5,000+ subroutines / 700,000+
lines of F77 code to C++. I have converted 23,000 lines so far. The
Fortran character strings to C strings or C++ STL strings are very
difficult.

Lynn

On 11 Nov 2022, Lynn McGuire wrote
(in article <tkmbmk$uc0u$3@dont-email.me>):

> On 11/11/2022 8:13 AM, Michael F. Stemper wrote:
> > On 10/11/2022 18.12, Lynn McGuire wrote:
> > > On 11/10/2022 10:07 AM, rkshullat@rosettacondot.com wrote:
> > > > peterwezeman@hotmail.com<peterwezeman@hotmail.com> wrote:
> >
> > > > > One possible source of confusion is that horizontal speeds are often
> > > > > given in miles per hour or kilometers
> > > > > hour whereas accelerations are given in feet per second per second
> > > > > or meters per second per second.
> > > > > As Michael Stemper suggests, try keeping the units consistent.
> > > >
> > > > When my wife and I were in college our physics professors put a lot of
> > > > emphasis on dimensional analysis:
> > > > <https://en.wikipedia.org/wiki/Dimensional_analysis>
> > > > She's continued the tradition with her students.
> > > > Getting the units right isn't a guarantee that you're correct but
> > > > getting them
> > > > wrong pretty much ensures that you're incorrect.
> > > > My into physics professor loved to give problems in unusual units
> > > > with the
> > > > answer in a different set (start with meters and hours and calculate
> > > > velocity
> > > > in furlongs per fortnight). You learned very quickly to convert to
> > > > consistent
> > > > units and carry those all the way through.
> >
> > > Keeping dimensional units correct is the hardest thing to do in our
> > > software. The old portion of the software is lbmol, R, psia, feet,
> > > etc. Other portions are kgmol or gmmol, K, kg/cm2 or pascal, meter,
> > > etc. Things can get dicey in a hurry.
> >
> > I know that you have a large existing code base in FORTRAN. However,
> > you might be interested (for future development) in this python module,
> > which does arithmetic on dimensioned quantities:
> > <https://pypi.org/project/units/>
> >
> > It supports standard units, as well as allowing you to roll your own.
> >
> > Headline:
> >
> > Provides support for quantities and units, which strictly disallow
> > invalid
> > operations between incompatible quantities. For example, we cannot
> > add 2 metres
> > to 5 seconds, because this doesn’t make sense.
>
> I am in the beginning of converting my 5,000+ subroutines / 700,000+
> lines of F77 code to C++. I have converted 23,000 lines so far. The
> Fortran character strings to C strings or C++ STL strings are very
> difficult.
>
> Lynn

Heh. I once converted a whole lot of FORTRAN77 to Modula-2. It wasn’t
pretty. I did it using a Modula-2 system on the Macintosh Programmer’s
Worksop system... 1986! The FORTRAN was originally a command-line program,
written for a Prime minicomputer! That project crashed and burned...

I still have MPW and Modula-2, on an ancient PowerMac G3. MPW runs in
Classic, the G3 can’t go beyond OS X 10.2.x, and can boot OS 9.2.x. I
haven’t actually fired MPW up in over a decade.

Modula-2 was quite bad enough. Hell freezes over before I try that on C++.

On the other hand, I do have a C++ compiler for MPW, and another, much newer,
one for XCode. Hmmm... Nope. Not doing it.

Robert Carnegie <rja.carnegie@excite.com> wrote in
news:42b6093e-4b8f-4de1-8e72-08fea528e309n@googlegroups.com:

> On Thursday, 10 November 2022 at 19:24:51 UTC, Scott Lurndal
> wrote:
>> David Brown <davidn...@gmail.com> writes:
>> >On Thursday, November 10, 2022 at 7:31:10 AM UTC-7, Scott
>> >Lurndal wrote:
>> >> David Brown <davidn...@gmail.com> writes:=20
>> >> >On Wednesday, November 9, 2022 at 4:21:59 PM UTC-7, Wolffan
>> >> >wrote:
>> >> <snip long physics lesson>
>> >> >> > crew many times over. What am I missing here???
>> >> >> yes. You accel at, say, 1 gee, and you get to anywhere in
>> >> >> the system i=
>> >n u=3D=20
>> >> >nder=3D20=20
>> >> >> a month and a half. One gee. You=3DE2=3D80=3D99re mixing
>> >> >> up velocity a=
>> >nd accele=3D=20
>> >> >ration.=3D20=20
>> >> >>=3D20
>> >> >> May I suggest a basic course on statics and dynamics?
>> >> >> >=3D20=20
>> >> >> >=3D20=20
>> >> >> > David N. Brown=3D20=20
>> >> >> > Mesa, Arizona=20
>> >> >I have ridiculously detailed and probably incoherent specs
>> >> >for the ship =
>> >in =3D=20
>> >> >chapters posted on my blog. It's called the Janus, and my
>> >> >head descripti=
>> >on =3D=20
>> >> >is Tinker Toy ship. My specs have been 360 m long (cut down
>> >> >from my very=
>> > fi=3D=20
>> >> >rst ideas) and 40-60 meters wide at one or two places
>> >> >including a Von Br=
>> >aun=3D
>> >> > style ring for artificial gravity.
>> >> So many 'spaceship' designs follow terrestrial
>> >> characteristics (i.e. typi=
>> >cally=20
>> >> cylindrical, or in the case of Star Wars, et. al.,
>> >> space-born aircraft ca=
>> >rriers).=20
>> >>=20
>> >> For spaceships that never intend to fly -in- atmosphere, it
>> >> would seem th=
>> >at the sphere=20
>> >> is the optimal form factor (given structural loading from
>> >> internal atomsp=
>> >heric pressure),=20
>> >> and the movie form (e.g. star wars) would be far from
>> >> optimal.=20
>> >>=20
>> >> The enterprise is pretty, but not particularly optimal,
>> >> particularly the=
>> >=20
>> >> saucer section.
>> >I've been a defender of the old-fashioned flying saucer, at
>> >least in its tr= uly radial variations. It lets you keep the
>> >command center and vital system= s in a small area, while
>> >still allowing you to spread the engines, sensors = and
>> >weapons (if any) across a 360 arc. Also, if there's incoming
>> >debris or = actual weapons fire, there's still one axis that's
>> >mostly flat. Ironically,=
>> > the Millennium Falcon is the one cinematic ship to be shown
>> > taking advanta=
>> >ge of these characteristics, and it still had some terrible
>> >design features=
>> > (partly because the life-sized sets had been created for a
>> > completely diff=
>> >erent ship).
>>
>> Your typical tube airliner (e.g. 737) has an internal pressure
>> of 11psi at a cruising altitude of 35,000 feet where the
>> external pressure is less than 4psi. That's over 7 pounds per
>> square inch of pressure on the internal cabin area
>> that needs to be designed for; the rear bulkhead, for instance
>> is dome shaped, rather than flat.
>>
>>
>> https://aviation.stackexchange.com/questions/31292/why-do-airlin
>> ers-have-pressure-bulkheads
>>
>> "The shape of the final aft section is not well suited to
>> resist pressurization stresses: the best shape is a sphere; the
>> cylinder (with spherical terminations) comes a close second.
>> The conical shape would require serious stiffeners to survive
>> pressurization cycles for the whole life of the aircraft; the
>> bulkhead solves this problem by using a shape that is naturally
>> more resistant to stresses - and thus can be built with less
>> material - leading to less weight, and hence fuel savings (in
>> addition to the increased safety)."
>>
>> "It's worth making a rough estimate of just how big the force
>> on such a bulkhead is. At sea level, atmospheric pressure of
>> 14.7 psi is roughly the same as 1 ton per square foot. The
>> difference between the internal and external pressure at
>> cruising altitude is about half that value. The fuselage
>> diameter of a B777 is about 20 feet, so the area of the
>> bulkhead is about 300 square feet. So the total force on the
>> bulkhead is about 150 tons. Compare that with the max takeoff
>> weight of the plane, which is about 250 tons - it's a seriously
>> large number."
>>
>> While a ship designed to remain in space permenently won't be
>> subjected to pressurization cycles, a spherical shape will
>> continue to be optimal to deal with stresses.
>>
>> Question: What affect does acceleration have on the atmosphere
>> within the spaceship?
>
> Logically (after Einstein), it's the same as the effect of
> gravity. Considered as a "traditional" rocket, air pressure is
> less at the "top" end than at the bottom. !I mean, if your
> spaceship is big enough for this to be inconvenient, then you
> have decks pressurized independently.

For a very graphic example of how acceleration affects air inside a
moving vehicle, go watch this video of a helium baloon tethered
inside a van:

https://www.youtube.com/watch?v=y8mzDvpKzfY

--
Terry Austin

"Terry Austin: like the polio vaccine, only with more asshole."
-- David Bilek

Jesus forgives sinners, not criminals.

Hamish Laws <hamish.laws@gmail.com> wrote in
news:7db26c10-a312-4300-bf10-8939d983a961n@googlegroups.com:

> On Thursday, November 10, 2022 at 6:35:42 AM UTC+11,
> peterwezeman@hotmail.com wrote:
>> On Wednesday, November 9, 2022 at 10:41:50 AM UTC-6, Michael F.
>> Stemper w
> rote:
>> > On 09/11/2022 10.21, David Brown wrote:
>> > > Here's something I've been working on for a retro future
>> > > project with
> hard sci fi elements. It calls for a gigantic 300+ meter ship
> to accelerate to 250,000 miles for a trip to the outer solar
> system, which I arm waved to maybe +12,000 miles of
> acceleration per day. Here's the weird thing. Regular
> terrestrial cars can accelerate 0-60 in 10 seconds without even
> being considered that fast, which comes out at 1 mile per
> second. That means if all conventional limitations were removed
> (friction, cooling, controllability, fuel supply, etc), the car
> could accelerate to 86,400 mph in 24 hours. The monkey wrench
> is, 1 G of acceleration amounts to a change of only 35 kph or
> 21 miles per hour, and people aren't supposed to be able
> survive 10 G of acceleration for more than a few seconds.
> Therefore, a manned vehicle accelerating at +5040 miles per
> hour every 24 hours would already kill the crew many times
> over. What am I missing here???
>> > If you're going to try to do hard science, you need to start
>> > by underst
> anding
>> > units of measure. One accelerates to a velocity (speed). You
>> > have your
> ship
>> > accelerating to a distance -- 250000 miles. That means that
>> > after it ha
> s gone
>> > that far it stops accelerating.
>> >
>> > I think that you probably want it to accelerate up to some
>> > speed, such
> as:
>> > - 250000 miles/year
>> > - 250000 miles/month
>> > - 250000 miles/day
>> > - 250000 miles/hour
>> > Something like one of those.
>> >
>> > For instance, let's take a look at your car example. When you
>> > discuss a
> car
>> > accelerating from 0-60, it means from 0 miles per hour to 60
>> > miles per
> hour,
>> > two speeds. That change in speed, if spread out evenly over a
>> > ten-secon
> d
>> > interval, would not be one mile per second (as you stated),
>> > but six mil
> es per
>> > hour per second.
>> >
>> > I think that you need to sit down with pencil and paper and
>> > work throug
> h all
>> > of this, making the units explicit throughout your work.
>> >
>> > Getting to your last question, the units are correct here
>> > (although I h
> ave
>> > no idea whether it's consistent with anything that went
>> > before).
>> >
>> > 5040 miles per hour per day works out to 210 miles per hour
>> > per hour, w
> hich
>> > means that over a period of one hour, you've sped up by 210
>> > miles per h
> our.
>> > If you think about it, a commercial airliner speeds up from
>> > stopped on
> the
>> > tarmac to a speed speed of over 500 miles per hour in a
>> > matter of ten m
> inutes
>> > or so, which is an acceleration of about 3000 miles per hour
>> > per hour,
> or
>> > much greater than what is mentioned here.
>> >
>> > By the way, this would be much less subject to error if you
>> > did your wo
> rk
>> > exclusively in meters and seconds.
>> This reminds me of a story. Someone bought a high-performance
>> Italian sports car, and was showing it to her friend, another
>> enthusiast, for the
>
>> first time. After riding as a passenger over some challenging
>> roads it was his turn to drive. Taking the driver's seat, he
>> listened attentively
> to
>> her pointers. Before they started off she said, "And remember,
>> the speedometer is calibrated in metric units."
>>
>> He let in the clutch and accelerated cautiously to 60, getting
>> the feel o
> f
>> the car. After a short time he asked, "Have you checked the
>> speedometer
>
>> with a stopwatch? I've driven in Europe, and it sure seems to
>> me that we're going faster than sixty kilometers per hour."
>>
>> She replied, "We are. That's meters per second."
>>
> 60 kmph is 16.67 mps
> 60 mps is 216 kmph
>
> I'll admit that a car can feel very different at speeds (I was
> badly fooled by a work car once) but that difference in speed
> should be readily apparent from visual cues
>
Trying to analyze the punch line of a joke does not make you looks
smart.

--
Terry Austin

"Terry Austin: like the polio vaccine, only with more asshole."
-- David Bilek

Jesus forgives sinners, not criminals.

Dimensional Traveler <dtravel@sonic.net> wrote in
news:tkluba$subg$1@dont-email.me:

> On 11/11/2022 8:27 AM, pyotr filipivich wrote:
>> scott@slp53.sl.home (Scott Lurndal) on Thu, 10 Nov 2022
>> 19:24:46 GMT typed in rec.arts.sf.written the following:
>>>
>>> While a ship designed to remain in space permenently won't be
>>> subjected to pressurization cycles, a spherical shape will
>>> continue to be optimal to deal with stresses.
>>
>> A ship in space is not completely free of pressurization
>> cycles.
>> Air locks for example. Atmospheric "sloshing" as it starts and
>> stops acceleration.
>>>
>>> Question: What affect does acceleration have on the
>>> atmosphere within the spaceship?
>>
>> It piles up at the "bottom" (along with the dust). Which
>> in a
>> small compartment may not be all that much floor to ceiling.
>> But an open corridor the length of a ship may get some serious
>> differential. Depends on A) ship's environmental pressure and
>> B) acceleration.
>>
>> Practical matters aside, how little acceleration do humans
>> need to
>> "function". Somewhere less than the surface gravity of the moon
>> is what I think.
>
> I think that last depends on your definition of "function" and
> for how long. Just visit and work for a few days or weeks? Do
> yearly rotations? Live there permanently?
>
> We already know from experience with the ISS that a year or less
> in micro-gravity can have permanent medical/health effects. I
> suspect that the longer one expects humans to stay there the
> closer to 1G the environment needs to be for them to remain
> "functional".
>
I think the people who actually do such things will carefully
disstinguist between "functional" and "healthy."

--
Terry Austin

"Terry Austin: like the polio vaccine, only with more asshole."
-- David Bilek

Jesus forgives sinners, not criminals.