In message <stgb4i$fo$1@dont-email.me>, at 10:34:58 on Thu, 3 Feb 2022,
Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> remarked:

>>> Or the upstream side of the embankment was washed away first, causing the
>>> rest of the embankment and the rails to slide that way. I think this has
>>> been suggested in other subthreads already.
>>
>> Yes, it's just that Roland keeps ignoring it.

I'm not ignoring the suggestion, just challenging the soil mechanics
underpinning it.

>Yes, looking back it was Anna, and they’ve[1] just repeated it.

--
Roland Perry

In message <stgfia$ta5$1@dont-email.me>, at 11:50:35 on Thu, 3 Feb 2022,
ColinR <rail@greystane.shetland.co.uk> remarked:
>On 03/02/2022 10:26, Anna Noyd-Dryver wrote:

> It's not Hornby "long straight" rigid track

>> which can be used as a bridge without any further support!
>>
>
>Now that is a good idea, why does not British Railways do that? ;-)

The track at Dawlish (2014) in a sense self-supported (not enough to
carry a train, obviously) and drooped, rather than heading off towards
the sea. And surely the side next to the sea was what eroded first.
--
Roland Perry

In message <stgal4$t5h$1@dont-email.me>, at 10:26:45 on Thu, 3 Feb 2022,
Anna Noyd-Dryver <anna@noyd-dryver.com> remarked:

>>> If you watch a stream of water cutting a channel, it’s usually the
>>>upstream end of the channel that gets the most energetic erosion.
>>
>> Yes, but why does that cause lateral slewing (upstream), rather than
>> more droop?
>
>Because the upstream side of the track gets eroded-under first, before the
>other side of the track. So the track is unsupported under one side only;
>has non-zero weight and is not a rigid structure. Why do you think it
>*wouldn't* slew to one side? It's not Hornby "long straight" rigid track
>which can be used as a bridge without any further support!

Slewing requires a horizontal force perpendicular to the track, and what
is providing that force. Drooping requires gravity acting downwards, and
that's in plentiful supply.
--
Roland Perry

Roland Perry <roland@perry.co.uk> wrote:
> In message <stg84j$cr0$2@dont-email.me>, at 09:43:47 on Thu, 3 Feb 2022,
> Recliner <recliner.usenet@gmail.com> remarked:
>
>>>> If you watch a stream of water cutting a channel, it’s usually the
>>>> upstream end of the channel that gets the most energetic erosion.
>>>
>>> Yes, but why does that cause lateral slewing (upstream), rather than
>>> more droop?
>>
>> The collapsing embankment would first have slid sideways into the water,
>> rather than descending vertically. There wasn't a through flow of water at
>> that stage, so no upstream or downstream.
>
> As soon as the embankment has crumbled below the level of the sleepers,
> which isn't much, then the only force on the track is gravity -
> downwards.

As soon as one side of the embankment has crumbled the track will slide in
that direction. Or does Perryworld physics ensure that the ground stays
completely level as it is eroded away?

Sam

--
The entity formerly known as Sam.Wilson@ed.ac.uk
Spit the dummy to reply

Roland Perry <roland@perry.co.uk> wrote:
> In message <stg84j$cr0$2@dont-email.me>, at 09:43:47 on Thu, 3 Feb 2022,
> Recliner <recliner.usenet@gmail.com> remarked:
>
>>>> If you watch a stream of water cutting a channel, it’s usually the
>>>> upstream end of the channel that gets the most energetic erosion.
>>>
>>> Yes, but why does that cause lateral slewing (upstream), rather than
>>> more droop?
>>
>> The collapsing embankment would first have slid sideways into the water,
>> rather than descending vertically. There wasn't a through flow of water at
>> that stage, so no upstream or downstream.
>
> As soon as the embankment has crumbled below the level of the sleepers,
> which isn't much, then the only force on the track is gravity -
> downwards.
>

The crumbling of the embankment will have been a gradual process, not
immediate across the entire width; for part of that time, one side of the
track was supported and the other side was unsupported. The unsupported
side gets affected by gravity, the track tilts and gravity once again
affects it and it slides sideways a certain extent.

You can see that clearly in this photo
<https://twitter.com/greatnorthroad2/status/1487801794327728129?s=21>

Anna Noyd-Dryver

Roland Perry <roland@perry.co.uk> wrote:
> In message <stg922$iiu$1@dont-email.me>, at 09:59:30 on Thu, 3 Feb 2022,
> Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> remarked:
>
>>>>> If you watch a stream of water cutting a channel, it’s usually
>>>>> the upstream end of the channel that gets the most energetic erosion.
>>>>
>>>> Yes, but why does that cause lateral slewing (upstream), rather than
>>>> more droop?
>>>
>>> The collapsing embankment would first have slid sideways into the water,
>>> rather than descending vertically. There wasn't a through flow of water at
>>> that stage, so no upstream or downstream.
>>
>> Or the upstream side of the embankment was washed away first, causing the
>> rest of the embankment and the rails to slide that way. I think this has
>> been suggested in other subthreads already.
>
> So I can understand your model, where and how was the upstream side
> washed away. By and along the main river, and not perpendicular?
>

Water started to penetrate the embankment somehow (weakness, or an existing
culvert which became blocked or overloaded?). Once this flow was
established, erosion was greatest at the point of entry, creating a funnel
shape.

Anna Noyd-Dryver

Roland Perry <roland@perry.co.uk> wrote:
> In message <stgal4$t5h$1@dont-email.me>, at 10:26:45 on Thu, 3 Feb 2022,
> Anna Noyd-Dryver <anna@noyd-dryver.com> remarked:
>
>>>> If you watch a stream of water cutting a channel, it’s usually the
>>>> upstream end of the channel that gets the most energetic erosion.
>>>
>>> Yes, but why does that cause lateral slewing (upstream), rather than
>>> more droop?
>>
>> Because the upstream side of the track gets eroded-under first, before the
>> other side of the track. So the track is unsupported under one side only;
>> has non-zero weight and is not a rigid structure. Why do you think it
>> *wouldn't* slew to one side? It's not Hornby "long straight" rigid track
>> which can be used as a bridge without any further support!
>
> Slewing requires a horizontal force perpendicular to the track, and what
> is providing that force. Drooping requires gravity acting downwards, and
> that's in plentiful supply.

The imbalance of force is provided by the erosion being initially
predominantly under one side only of the track.

Anna Noyd-Dryver

Roland Perry <roland@perry.co.uk> wrote:
> In message <stgfia$ta5$1@dont-email.me>, at 11:50:35 on Thu, 3 Feb 2022,
> ColinR <rail@greystane.shetland.co.uk> remarked:
>> On 03/02/2022 10:26, Anna Noyd-Dryver wrote:
>
>> It's not Hornby "long straight" rigid track
>
>>> which can be used as a bridge without any further support!
>>>
>>
>> Now that is a good idea, why does not British Railways do that? ;-)
>
> The track at Dawlish (2014) in a sense self-supported (not enough to
> carry a train, obviously) and drooped, rather than heading off towards
> the sea. And surely the side next to the sea was what eroded first.
>

Dawlish was a very different process; waves overtopping the wall flooded
the trackbed to the extent that the wall could no longer support the
weight, and the wall collapsed outward.

Anna Noyd-Dryver

Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
> Roland Perry <roland@perry.co.uk> wrote:
>> In message <stgal4$t5h$1@dont-email.me>, at 10:26:45 on Thu, 3 Feb 2022,
>> Anna Noyd-Dryver <anna@noyd-dryver.com> remarked:
>>
>>>>> If you watch a stream of water cutting a channel, it’s usually the
>>>>> upstream end of the channel that gets the most energetic erosion.
>>>>
>>>> Yes, but why does that cause lateral slewing (upstream), rather than
>>>> more droop?
>>>
>>> Because the upstream side of the track gets eroded-under first, before the
>>> other side of the track. So the track is unsupported under one side only;
>>> has non-zero weight and is not a rigid structure. Why do you think it
>>> *wouldn't* slew to one side? It's not Hornby "long straight" rigid track
>>> which can be used as a bridge without any further support!
>>
>> Slewing requires a horizontal force perpendicular to the track, and what
>> is providing that force. Drooping requires gravity acting downwards, and
>> that's in plentiful supply.
>
> The imbalance of force is provided by the erosion being initially
> predominantly under one side only of the track.
>
>
> Anna Noyd-Dryver
>
>

If you put a marble on a slope the only force according to Roland is just
downwards gravity. Yet as the marble rolls down the hill it moves both
vertically and horizontally.

The eroded track length is effectively rolling down hill (well not rolling
but you know what I mean).

On 03/02/2022 18:19, Anna Noyd-Dryver wrote:
> Roland Perry <roland@perry.co.uk> wrote:
>> In message <stg84j$cr0$2@dont-email.me>, at 09:43:47 on Thu, 3 Feb 2022,
>> Recliner <recliner.usenet@gmail.com> remarked:
>>
>>>>> If you watch a stream of water cutting a channel, it’s usually the
>>>>> upstream end of the channel that gets the most energetic erosion.
>>>>
>>>> Yes, but why does that cause lateral slewing (upstream), rather than
>>>> more droop?
>>>
>>> The collapsing embankment would first have slid sideways into the water,
>>> rather than descending vertically. There wasn't a through flow of water at
>>> that stage, so no upstream or downstream.
>>
>> As soon as the embankment has crumbled below the level of the sleepers,
>> which isn't much, then the only force on the track is gravity -
>> downwards.
>
> The crumbling of the embankment will have been a gradual process, not
> immediate across the entire width; for part of that time, one side of the
> track was supported and the other side was unsupported. The unsupported
> side gets affected by gravity, the track tilts and gravity once again
> affects it and it slides sideways a certain extent.
>
> You can see that clearly in this photo
> <https://twitter.com/greatnorthroad2/status/1487801794327728129?s=21>

Yes. A hill appears, and the track slides down it. Being Norfolk, it's
a one-foot hill, but it's enough to move the rails sideways.

Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
> Roland Perry <roland@perry.co.uk> wrote:
>> In message <stg84j$cr0$2@dont-email.me>, at 09:43:47 on Thu, 3 Feb 2022,
>> Recliner <recliner.usenet@gmail.com> remarked:
>>
>>>>> If you watch a stream of water cutting a channel, it’s usually the
>>>>> upstream end of the channel that gets the most energetic erosion.
>>>>
>>>> Yes, but why does that cause lateral slewing (upstream), rather than
>>>> more droop?
>>>
>>> The collapsing embankment would first have slid sideways into the water,
>>> rather than descending vertically. There wasn't a through flow of water at
>>> that stage, so no upstream or downstream.
>>
>> As soon as the embankment has crumbled below the level of the sleepers,
>> which isn't much, then the only force on the track is gravity -
>> downwards.
>>
>
> The crumbling of the embankment will have been a gradual process, not
> immediate across the entire width; for part of that time, one side of the
> track was supported and the other side was unsupported. The unsupported
> side gets affected by gravity, the track tilts and gravity once again
> affects it and it slides sideways a certain extent.
>
> You can see that clearly in this photo
> <https://twitter.com/greatnorthroad2/status/1487801794327728129?s=21>
>

Yes, that's an excellent demonstration, which conclusively proves what
happened.

On 03/02/2022 19:49, Certes wrote:
> On 03/02/2022 18:19, Anna Noyd-Dryver wrote:
>> Roland Perry <roland@perry.co.uk> wrote:
>>> In message <stg84j$cr0$2@dont-email.me>, at 09:43:47 on Thu, 3 Feb 2022,
>>> Recliner <recliner.usenet@gmail.com> remarked:
>>>
>>>>>> If you watch a stream of water cutting a channel, it’s usually the
>>>>>> upstream  end of the channel that gets the most energetic erosion.
>>>>>
>>>>> Yes, but why does that cause lateral slewing (upstream), rather than
>>>>> more droop?
>>>>
>>>> The collapsing embankment would first have slid sideways into the
>>>> water,
>>>> rather than descending vertically. There wasn't a through flow of
>>>> water at
>>>> that stage, so no upstream or downstream.
>>>
>>> As soon as the embankment has crumbled below the level of the sleepers,
>>> which isn't much, then the only force on the track is gravity -
>>> downwards.
>>
>> The crumbling of the embankment will have been a gradual process, not
>> immediate across the entire width; for part of that time, one side of the
>> track was supported and the other side was unsupported. The unsupported
>> side gets affected by gravity, the track tilts and gravity once again
>> affects it and it slides sideways a certain extent.
>>
>> You can see that clearly in this photo
>> <https://twitter.com/greatnorthroad2/status/1487801794327728129?s=21>
>
> Yes.  A hill appears, and the track slides down it.  Being Norfolk, it's
> a one-foot hill, but it's enough to move the rails sideways.

Good grief, has logic silenced the Perry??

--
Colin

ColinR <rail@greystane.shetland.co.uk> wrote:
> On 03/02/2022 19:49, Certes wrote:
>> On 03/02/2022 18:19, Anna Noyd-Dryver wrote:
>>> Roland Perry <roland@perry.co.uk> wrote:
>>>> In message <stg84j$cr0$2@dont-email.me>, at 09:43:47 on Thu, 3 Feb 2022,
>>>> Recliner <recliner.usenet@gmail.com> remarked:
>>>>
>>>>>>> If you watch a stream of water cutting a channel, it’s usually the
>>>>>>> upstream  end of the channel that gets the most energetic erosion.
>>>>>>
>>>>>> Yes, but why does that cause lateral slewing (upstream), rather than
>>>>>> more droop?
>>>>>
>>>>> The collapsing embankment would first have slid sideways into the
>>>>> water,
>>>>> rather than descending vertically. There wasn't a through flow of
>>>>> water at
>>>>> that stage, so no upstream or downstream.
>>>>
>>>> As soon as the embankment has crumbled below the level of the sleepers,
>>>> which isn't much, then the only force on the track is gravity -
>>>> downwards.
>>>
>>> The crumbling of the embankment will have been a gradual process, not
>>> immediate across the entire width; for part of that time, one side of the
>>> track was supported and the other side was unsupported. The unsupported
>>> side gets affected by gravity, the track tilts and gravity once again
>>> affects it and it slides sideways a certain extent.
>>>
>>> You can see that clearly in this photo
>>> <https://twitter.com/greatnorthroad2/status/1487801794327728129?s=21>
>>
>> Yes.  A hill appears, and the track slides down it.  Being Norfolk, it's
>> a one-foot hill, but it's enough to move the rails sideways.
>
> Good grief, has logic silenced the Perry??

Unlikely. He saves up his responses to reply in a batch. Expect a flurry
in the morning.

Sam

--
The entity formerly known as Sam.Wilson@ed.ac.uk
Spit the dummy to reply

Certes <none@nowhere.net> wrote:
>
> Yes. A hill appears, and the track slides down it. Being Norfolk, it's
> a one-foot hill, but it's enough to move the rails sideways.
>

A molehill compared to elsewhere then , that Roland is making a mountain
of.

GH

In message <sth6ba$35c$4@dont-email.me>, at 18:19:22 on Thu, 3 Feb 2022,
Anna Noyd-Dryver <anna@noyd-dryver.com> remarked:
>Roland Perry <roland@perry.co.uk> wrote:
>> In message <stgfia$ta5$1@dont-email.me>, at 11:50:35 on Thu, 3 Feb 2022,
>> ColinR <rail@greystane.shetland.co.uk> remarked:
>>> On 03/02/2022 10:26, Anna Noyd-Dryver wrote:
>>
>>> It's not Hornby "long straight" rigid track
>>
>>>> which can be used as a bridge without any further support!
>>>>
>>>
>>> Now that is a good idea, why does not British Railways do that? ;-)
>>
>> The track at Dawlish (2014) in a sense self-supported (not enough to
>> carry a train, obviously) and drooped, rather than heading off towards
>> the sea. And surely the side next to the sea was what eroded first.
>
>Dawlish was a very different process; waves overtopping the wall flooded
>the trackbed to the extent that the wall could no longer support the
>weight, and the wall collapsed outward.

Exactly. Why didn't the track follow it, sideways?
--
Roland Perry

In message <sth7uq$f0i$1@dont-email.me>, at 18:46:50 on Thu, 3 Feb 2022,
Tweed <usenet.tweed@gmail.com> remarked:
>Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
>> Roland Perry <roland@perry.co.uk> wrote:
>>> In message <stgal4$t5h$1@dont-email.me>, at 10:26:45 on Thu, 3 Feb 2022,
>>> Anna Noyd-Dryver <anna@noyd-dryver.com> remarked:
>>>
>>>>>> If you watch a stream of water cutting a channel, it’s usually the
>>>>>> upstream end of the channel that gets the most energetic erosion.
>>>>>
>>>>> Yes, but why does that cause lateral slewing (upstream), rather than
>>>>> more droop?
>>>>
>>>> Because the upstream side of the track gets eroded-under first, before the
>>>> other side of the track. So the track is unsupported under one side only;
>>>> has non-zero weight and is not a rigid structure. Why do you think it
>>>> *wouldn't* slew to one side? It's not Hornby "long straight" rigid track
>>>> which can be used as a bridge without any further support!
>>>
>>> Slewing requires a horizontal force perpendicular to the track, and what
>>> is providing that force. Drooping requires gravity acting downwards, and
>>> that's in plentiful supply.
>>
>> The imbalance of force is provided by the erosion being initially
>> predominantly under one side only of the track.
>
>If you put a marble on a slope the only force according to Roland is just
>downwards gravity. Yet as the marble rolls down the hill it moves both
>vertically and horizontally.
>
>The eroded track length is effectively rolling down hill (well not rolling
>but you know what I mean).

If the ground under the track has eroded by more than about six inches,
there isn't a slope for the track to slide down. It's just hanging in
mid air.
--
Roland Perry

In message <sth6b9$35c$2@dont-email.me>, at 18:19:21 on Thu, 3 Feb 2022,
Anna Noyd-Dryver <anna@noyd-dryver.com> remarked:
>Roland Perry <roland@perry.co.uk> wrote:
>> In message <stg922$iiu$1@dont-email.me>, at 09:59:30 on Thu, 3 Feb 2022,
>> Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> remarked:
>>
>>>>>> If you watch a stream of water cutting a channel, it’s usually
>>>>>> the upstream end of the channel that gets the most energetic erosion.
>>>>>
>>>>> Yes, but why does that cause lateral slewing (upstream), rather than
>>>>> more droop?
>>>>
>>>> The collapsing embankment would first have slid sideways into the water,
>>>> rather than descending vertically. There wasn't a through flow of water at
>>>> that stage, so no upstream or downstream.
>>>
>>> Or the upstream side of the embankment was washed away first, causing the
>>> rest of the embankment and the rails to slide that way. I think this has
>>> been suggested in other subthreads already.
>>
>> So I can understand your model, where and how was the upstream side
>> washed away. By and along the main river, and not perpendicular?
>
>Water started to penetrate the embankment somehow (weakness, or an existing
>culvert which became blocked or overloaded?). Once this flow was
>established, erosion was greatest at the point of entry, creating a funnel
>shape.

Was the eroded material washed perpendicularly through the funnel, or
along the line of the main river?
--
Roland Perry

In message <sth498$jih$1@dont-email.me>, at 17:44:08 on Thu, 3 Feb 2022,
Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> remarked:
>Roland Perry <roland@perry.co.uk> wrote:
>> In message <stg84j$cr0$2@dont-email.me>, at 09:43:47 on Thu, 3 Feb 2022,
>> Recliner <recliner.usenet@gmail.com> remarked:
>>
>>>>> If you watch a stream of water cutting a channel, it’s usually the
>>>>> upstream end of the channel that gets the most energetic erosion.
>>>>
>>>> Yes, but why does that cause lateral slewing (upstream), rather than
>>>> more droop?
>>>
>>> The collapsing embankment would first have slid sideways into the water,
>>> rather than descending vertically. There wasn't a through flow of water at
>>> that stage, so no upstream or downstream.
>>
>> As soon as the embankment has crumbled below the level of the sleepers,
>> which isn't much, then the only force on the track is gravity -
>> downwards.
>
>As soon as one side of the embankment has crumbled the track will slide in
>that direction. Or does Perryworld physics ensure that the ground stays
>completely level as it is eroded away?

As soon as ground is below the level of the bottom of the sleepers,
there's no slope down which to slide.

And track isn't particularly elastic, to go both sideways and down
requires the metal rails to stretch more than I think the normally
would, in order to hug the changing ground level.

On the other hand, when a train arrives and creates drag via the brakes,
there's the whole momentum/weight of the train (which is considerably
more than the track itself) to cause the distortion.
--
Roland Perry

In message <sth6b9$35c$1@dont-email.me>, at 18:19:21 on Thu, 3 Feb 2022,
Anna Noyd-Dryver <anna@noyd-dryver.com> remarked:
>Roland Perry <roland@perry.co.uk> wrote:
>> In message <stg84j$cr0$2@dont-email.me>, at 09:43:47 on Thu, 3 Feb 2022,
>> Recliner <recliner.usenet@gmail.com> remarked:
>>
>>>>> If you watch a stream of water cutting a channel, it’s usually the
>>>>> upstream end of the channel that gets the most energetic erosion.
>>>>
>>>> Yes, but why does that cause lateral slewing (upstream), rather than
>>>> more droop?
>>>
>>> The collapsing embankment would first have slid sideways into the water,
>>> rather than descending vertically. There wasn't a through flow of water at
>>> that stage, so no upstream or downstream.
>>
>> As soon as the embankment has crumbled below the level of the sleepers,
>> which isn't much, then the only force on the track is gravity -
>> downwards.
>
>The crumbling of the embankment will have been a gradual process, not
>immediate across the entire width; for part of that time, one side of the
>track was supported and the other side was unsupported. The unsupported
>side gets affected by gravity, the track tilts and gravity once again
>affects it and it slides sideways a certain extent.
>
>You can see that clearly in this photo
><https://twitter.com/greatnorthroad2/status/1487801794327728129?s=21>

All we can see there is what happened as a result of the train arriving,
not what it looked like *before* the train arrived.
--
Roland Perry

In message <sthl4p$dtg$1@dont-email.me>, at 22:31:53 on Thu, 3 Feb 2022,
Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> remarked:

>> Good grief, has logic silenced the Perry??
>
>Unlikely. He saves up his responses to reply in a batch. Expect a flurry
>in the morning.

A flurry some morning. I'm afraid I don't have the time or energy to
reply in real time.
--
Roland Perry

Roland Perry <roland@perry.co.uk> wrote:
> In message <sth6ba$35c$4@dont-email.me>, at 18:19:22 on Thu, 3 Feb 2022,
> Anna Noyd-Dryver <anna@noyd-dryver.com> remarked:
>> Roland Perry <roland@perry.co.uk> wrote:
>>> In message <stgfia$ta5$1@dont-email.me>, at 11:50:35 on Thu, 3 Feb 2022,
>>> ColinR <rail@greystane.shetland.co.uk> remarked:
>>>> On 03/02/2022 10:26, Anna Noyd-Dryver wrote:
>>>
>>>> It's not Hornby "long straight" rigid track
>>>
>>>>> which can be used as a bridge without any further support!
>>>>>
>>>>
>>>> Now that is a good idea, why does not British Railways do that? ;-)
>>>
>>> The track at Dawlish (2014) in a sense self-supported (not enough to
>>> carry a train, obviously) and drooped, rather than heading off towards
>>> the sea. And surely the side next to the sea was what eroded first.
>>
>> Dawlish was a very different process; waves overtopping the wall flooded
>> the trackbed to the extent that the wall could no longer support the
>> weight, and the wall collapsed outward.
>
> Exactly. Why didn't the track follow it, sideways?

Because the ground underneath the track collapsed straight downwards as the
bottom of the wall blew out?

Also, we only saw very-much-after-the-event photos of Dawlish. At Haddiscoe
we saw pictures of the erosion as it was happening. Once the erosion
reaches a state where both sides of the gap are parallel, and the train is
removed, I would expect the tracks here to also hang in a straight line
between the two sides.

Anna Noyd-Dryver

Roland Perry <roland@perry.co.uk> wrote:
> In message <sth7uq$f0i$1@dont-email.me>, at 18:46:50 on Thu, 3 Feb 2022,
> Tweed <usenet.tweed@gmail.com> remarked:
>> Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
>>> Roland Perry <roland@perry.co.uk> wrote:
>>>> In message <stgal4$t5h$1@dont-email.me>, at 10:26:45 on Thu, 3 Feb 2022,
>>>> Anna Noyd-Dryver <anna@noyd-dryver.com> remarked:
>>>>
>>>>>>> If you watch a stream of water cutting a channel, it’s usually the
>>>>>>> upstream end of the channel that gets the most energetic erosion.
>>>>>>
>>>>>> Yes, but why does that cause lateral slewing (upstream), rather than
>>>>>> more droop?
>>>>>
>>>>> Because the upstream side of the track gets eroded-under first, before the
>>>>> other side of the track. So the track is unsupported under one side only;
>>>>> has non-zero weight and is not a rigid structure. Why do you think it
>>>>> *wouldn't* slew to one side? It's not Hornby "long straight" rigid track
>>>>> which can be used as a bridge without any further support!
>>>>
>>>> Slewing requires a horizontal force perpendicular to the track, and what
>>>> is providing that force. Drooping requires gravity acting downwards, and
>>>> that's in plentiful supply.
>>>
>>> The imbalance of force is provided by the erosion being initially
>>> predominantly under one side only of the track.
>>
>> If you put a marble on a slope the only force according to Roland is just
>> downwards gravity. Yet as the marble rolls down the hill it moves both
>> vertically and horizontally.
>>
>> The eroded track length is effectively rolling down hill (well not rolling
>> but you know what I mean).
>
> If the ground under the track has eroded by more than about six inches,
> there isn't a slope for the track to slide down. It's just hanging in
> mid air.

But at that point it had only eroded under *one side of the track*.

Anna Noyd-Dryver

In message <sto7bj$5cb$2@dont-email.me>, at 10:19:31 on Sun, 6 Feb 2022,
Anna Noyd-Dryver <anna@noyd-dryver.com> remarked:
>Roland Perry <roland@perry.co.uk> wrote:
>> In message <sth7uq$f0i$1@dont-email.me>, at 18:46:50 on Thu, 3 Feb 2022,
>> Tweed <usenet.tweed@gmail.com> remarked:
>>> Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
>>>> Roland Perry <roland@perry.co.uk> wrote:
>>>>> In message <stgal4$t5h$1@dont-email.me>, at 10:26:45 on Thu, 3 Feb 2022,
>>>>> Anna Noyd-Dryver <anna@noyd-dryver.com> remarked:
>>>>>
>>>>>>>> If you watch a stream of water cutting a channel, it’s usually the
>>>>>>>> upstream end of the channel that gets the most energetic erosion.
>>>>>>>
>>>>>>> Yes, but why does that cause lateral slewing (upstream), rather than
>>>>>>> more droop?
>>>>>>
>>>>>> Because the upstream side of the track gets eroded-under first,
>>>>>>before the
>>>>>> other side of the track. So the track is unsupported under one side only;
>>>>>> has non-zero weight and is not a rigid structure. Why do you think it
>>>>>> *wouldn't* slew to one side? It's not Hornby "long straight" rigid track
>>>>>> which can be used as a bridge without any further support!
>>>>>
>>>>> Slewing requires a horizontal force perpendicular to the track, and what
>>>>> is providing that force. Drooping requires gravity acting downwards, and
>>>>> that's in plentiful supply.
>>>>
>>>> The imbalance of force is provided by the erosion being initially
>>>> predominantly under one side only of the track.
>>>
>>> If you put a marble on a slope the only force according to Roland is just
>>> downwards gravity. Yet as the marble rolls down the hill it moves both
>>> vertically and horizontally.
>>>
>>> The eroded track length is effectively rolling down hill (well not rolling
>>> but you know what I mean).
>>
>> If the ground under the track has eroded by more than about six inches,
>> there isn't a slope for the track to slide down. It's just hanging in
>> mid air.
>
>But at that point it had only eroded under *one side of the track*.

Sure about that?

<https://i.dailymail.co.uk/1s/2022/01/30/18/53556263-10457643-image-m-
23_1643568862268.jpg>
--
Roland Perry

Roland Perry <roland@perry.co.uk> wrote:
> In message <sto7bj$5cb$2@dont-email.me>, at 10:19:31 on Sun, 6 Feb 2022,
> Anna Noyd-Dryver <anna@noyd-dryver.com> remarked:
>> Roland Perry <roland@perry.co.uk> wrote:
>>> In message <sth7uq$f0i$1@dont-email.me>, at 18:46:50 on Thu, 3 Feb 2022,
>>> Tweed <usenet.tweed@gmail.com> remarked:
>>>> Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
>>>>> Roland Perry <roland@perry.co.uk> wrote:
>>>>>> In message <stgal4$t5h$1@dont-email.me>, at 10:26:45 on Thu, 3 Feb 2022,
>>>>>> Anna Noyd-Dryver <anna@noyd-dryver.com> remarked:
>>>>>>
>>>>>>>>> If you watch a stream of water cutting a channel, it’s usually the
>>>>>>>>> upstream end of the channel that gets the most energetic erosion.
>>>>>>>>
>>>>>>>> Yes, but why does that cause lateral slewing (upstream), rather than
>>>>>>>> more droop?
>>>>>>>
>>>>>>> Because the upstream side of the track gets eroded-under first,
>>>>>>> before the
>>>>>>> other side of the track. So the track is unsupported under one side only;
>>>>>>> has non-zero weight and is not a rigid structure. Why do you think it
>>>>>>> *wouldn't* slew to one side? It's not Hornby "long straight" rigid track
>>>>>>> which can be used as a bridge without any further support!
>>>>>>
>>>>>> Slewing requires a horizontal force perpendicular to the track, and what
>>>>>> is providing that force. Drooping requires gravity acting downwards, and
>>>>>> that's in plentiful supply.
>>>>>
>>>>> The imbalance of force is provided by the erosion being initially
>>>>> predominantly under one side only of the track.
>>>>
>>>> If you put a marble on a slope the only force according to Roland is just
>>>> downwards gravity. Yet as the marble rolls down the hill it moves both
>>>> vertically and horizontally.
>>>>
>>>> The eroded track length is effectively rolling down hill (well not rolling
>>>> but you know what I mean).
>>>
>>> If the ground under the track has eroded by more than about six inches,
>>> there isn't a slope for the track to slide down. It's just hanging in
>>> mid air.
>>
>> But at that point it had only eroded under *one side of the track*.
>
> Sure about that?
>
> <https://i.dailymail.co.uk/1s/2022/01/30/18/53556263-10457643-image-m-
> 23_1643568862268.jpg>

That was taken later.

On 06/02/2022 09:27, Roland Perry wrote:
> In message <sthl4p$dtg$1@dont-email.me>, at 22:31:53 on Thu, 3 Feb 2022,
> Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> remarked:
>
>>> Good grief, has logic silenced the Perry??
>>
>> Unlikely.  He saves up his responses to reply in a batch.  Expect a
>> flurry
>> in the morning.
>
> A flurry some morning. I'm afraid I don't have the time or energy to
> reply in real time.

Oops, the box has opened.....

--
Colin