Stuck gear and entropy - physics question

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 josh12345 06 Jun 2019

Following a recent climb where I spent a lot of time fiddling with a piece of gear that did not want to come out (I got it eventually though) I got to pondering why, with respect to entropy, gear gets stuck.

Entropy is always trying to increase, and I understand entropy to be analogous to 'disorder', ie if something is stacked up it will fall over; things will collapse; demolition is easier than building...

So, to my mind, a piece of placed gear has a low entropy, and a piece of gear not in the rock has a high entropy, so why does gear get stuck? Surely it should want to come out?

I know its rather geeky but if anyone has a potential explanation or general philosophical musings on the subject I'd be very interested.

Thanks

1
 The Norris 06 Jun 2019
In reply to josh12345:

If a climber trying to remove a stuck nut is not a definition of chaos, I dont know what is!

 skog 06 Jun 2019
In reply to josh12345:

I'm not a physicist but...

I don't think entropy is directly driving the situation you describe, or at least not on the timescale you expect (the nut will not stay in the crack forever, even if you leave it). I'm not even sure that you're right in thinking that a 'nut in a crack' system has lower entropy than a 'nut lying around elsewhere' system.

Also, it's entirely possible to reduce entropy locally - it's just that you can't do so without increasing entropy by a greater (or at least equal) amount in the surroundings - e.g. you can cool something, but release more heat into the environment in the process; you can grow disorganised ions into crystals but doing so causes greater disorganisation around (e.g. by releasing heat). It's the entropy of the universe that appears to be always increasing.

 jkarran 06 Jun 2019
In reply to josh12345:

> Entropy is always trying to increase, and I understand entropy to be analogous to 'disorder', ie if something is stacked up it will fall over; things will collapse; demolition is easier than building...

Think about a tub of gravel, as you vibrate it it all settles, packing down losing height and potential energy. Your nut is like a piece of that gravel, as you jiggle it about randomly it tends to settle better into a placement.

> So, to my mind, a piece of placed gear has a low entropy, and a piece of gear not in the rock has a high entropy, so why does gear get stuck? Surely it should want to come out?

To be honest, I'm not convinced it has much to do with entropy, it's just that the better settled the nut gets the less it moves when you do break it free, the harder that moment is to notice, the harder the movement is to exploit deliberately then you pause and it settles back to another good or better seating. Often also you're pushing gear to loosen it, it breaks loose, moves back in the crack then re-seats somewhere harder to see, harder to reach.

jk

XXXX 06 Jun 2019
In reply to josh12345:

Ooh I know this one. It's because the situation as described is of no relevance to thermodynamics as we know it.

In reply to josh12345:

For a stuck nut to fall out, the rock or the aluminium would have to decay. Most rocks at the Earth's surface are way out of thermodynamic equilibrium and remain in a highly ordered (low entropy) crystalline state for millions (sometimes even billions) of years.

Whilst climbing, others physics is much more concerning than entropy - e.g. gravity.

1
 aln 06 Jun 2019
In reply to jkarran:

> Think about a tub of gravel, as you vibrate it it all settles, packing down losing height and potential energy. Your nut is like a piece of that gravel, as you jiggle it about randomly it tends to settle better into a placement.

That's brilliant, thanks.

 Siward 06 Jun 2019
In reply to XXXX:

But isn't my daughter's bedroom subject to entropy? Starts off clean and tidy, ends up impossible even to open the door so messy has it become?

1
 Jon Greengrass 06 Jun 2019
In reply to josh12345:

while the nut is stuck in the crack it is not neatly sorted by size and racked on your harness (high entropy ordered state) . Making the nut difficult to remove is the universe's way of lowering entropy.

Entropy also explains why we find that our gear has always been retrieved by someone else if we return to the crag another day to try to get it out again, because taking your nut to put on their rack where it doesn't belong is more out of order than it would be on your own rack.

 StuMsg 06 Jun 2019
In reply to josh12345:

I was recently at a crag where a presumably stuck nut (and for many years given the condition of it) was laying at the bottom of a crack that was clearly too big for a placement and also had a nice layer of soil over it. Where it was sitting was almost impossible for someone to just drop it from higher up and have it land there. The entire route is clearly in the process of falling down and it appears that after many years that crack had widened in the process of falling apart (increasing entropy) and the nut became loose in it's placement and ended where it was.

So Like Jon Greengrass mentioned, leave the gear long enough and it'll fall out and the cliff will fall down at some point too.

 wintertree 06 Jun 2019
In reply to XXXX:

> Ooh I know this one. It's because the situation as described is of no relevance to thermodynamics as we know it.

It absolutely is thermodynamics.  

That stuck cam has an average of 1/2 kB.t of thermal energy in every degree of freedom it possesses.  Global entropy was increased by the conversion of food to excreta that powered its placement.  More work was done to jiggle it to its stuck location.  In being stuck if probably lost some DOFs and so changed it’s heat capacity.

Thermodynamics is of little use here but it’s totally in play.

3
OP josh12345 06 Jun 2019
In reply to jkarran:

> Think about a tub of gravel, as you vibrate it it all settles, packing down losing height and potential energy. Your nut is like a piece of that gravel, as you jiggle it about randomly it tends to settle better into a placement.

Thanks, I think that's a really good explanation. In entropy terms, a bucket of unshaken and unsettled gravel has a lower entropy than the settled gravel, similar with the gear. To get the gear out requires entropy to be increased momentarily, which is why it requires energy and is a faff. The same as if you were to get a specific piece of gravel (say if one piece was painted) out of bucket.

2
OP josh12345 06 Jun 2019
In reply to josh12345:

Thanks for all the replies, they made me smile

OP josh12345 06 Jun 2019
In reply to Siward:

Yes, it takes more energy to put things away than drop them. Hence bedrooms become messier.

XXXX 06 Jun 2019
In reply to wintertree:

> It absolutely is thermodynamics.  

If you say so!

 wintertree 06 Jun 2019
In reply to XXXX:

> If you say so!

It’s currently very trendy in some circles to believe that the whole of reality is no more than thermodynamically governed information.

In reply to wintertree:

The kT energy and thermal degrees of freedom are on an atomic scale that is essentially unaffected by the cam being stuck - so the change in it's thermal capacity is negligible.

 Richard J 07 Jun 2019
In reply to John Stainforth:

That's right, temperature isn't important in this problem - the Brownian motion that an object has by virtue of its temperature, that is constantly shaking it around, is negligibly small for a macroscopic object like your stuck piece of gear.

But you can think of the problem in terms of something like an entropy - essentially, there's lots of orientations of the nut in which it's stuck, but only one orientation in which it will come out. So if you're hanging on randomly wiggling it, you have to go through lots of different orientations before you've got a chance of find the one in which you can free it.  It's your random wiggling that's playing the role that for a microscopic system would be played by temperature.  

The gravel analogy is a good one and in fact there are some modern theories of how sandpits work that start from that basic insight. 

 DaveHK 07 Jun 2019
In reply to josh12345:

As others have pointed out, entropy is of very little or no relevance here. Entropy works at a molecular level and the issue you raise with cams isn't described at a molecular level.

Although the word disorder is often used in explaining entropy it isn't actually a very helpful description as it leads us to think like you have about disorder in general terms, untidy houses and the like. It's a slippery concept for a number of reasons not least because there are several different ways of describing it.

Unless what your asking is how the cam situation might be seen as analogous to entropy?

Post edited at 06:50
 Michael Hood 07 Jun 2019
In reply to Siward:

The clearing up process is also a perfect example of how you can reverse entropy locally (daughter clearing up room) but there's at least a corresponding increase in entropy globally (the effort required to get her to tidy up, the moaning and ranting about having to do it, the thumping about whilst do it and the grumbling after completing it)

 Michael Hood 07 Jun 2019
In reply to josh12345:

Garages are also a marvelous example of order decaying into disorder

 wintertree 07 Jun 2019
In reply to John Stainforth:

> The kT energy and thermal degrees of freedom are on an atomic scale that is essentially unaffected by the cam being stuck - so the change in it's thermal capacity is negligible.

Obviously.  As I noted in my post. 

The entropy increase of doing work to make the gear stick was not so negligible however, as I also said in my post.

 My point being that everything about the cam’s journey to being stuck was thermodynamics - negligible or not it applies contrary to the post I was replying to.

In reply to josh12345:

One way of thinking about entropy is that it is a way of reaching the most stable level of energy or organisation. (heat death of the universe)

So realistically the stuck nut is more 'stable' where it is and you are fighting this situation by trying to bring it to a higher 'potential energy' ie putting it back on your rack.

So, in a way, entropy favours stuck nuts.

In reply to DubyaJamesDubya:

Normally we climb upwards, so if we leave nuts or cams stuck in a cliff we have increased potential energy. Nature will be trying to reverse that.

 Trevers 07 Jun 2019
In reply to josh12345:

I was climbing on the Cromlech once, seconding the top pitch of Dives/Better Things. As I was clipping a removed nut onto my harness, the nut worked its way free from the snapgate and dropped. I thought that was the last I'd ever see of it but duly stepped down to check and found the nut hanging precariously over the edge, caught delicately in some shrubbery. As I bent down to pick it up and return it to its rightful position on my harness, I found a second nut dropped by some previous passer-by hanging on right next to it with an even more tenuous hold to the crag.

I'm sure this reveals some deep, universal truth, but I don't think it has anything to do with entropy or the laws of thermodynamics.

Post edited at 12:50
 DaveHK 07 Jun 2019
In reply to Trevers:

>  I found a second nut dropped by some previous passer-by hanging on right next to it with an even more tenuous hold to the crag.

I once dropped a nut down a crack behind a block (sounds painful/rude) and couldn't get it back. On the next pitch we retrieved a stuck nut of the same size and make. I conclude from this that Jesus loves me.

In reply to John Stainforth:

That is true. But you could view the climber/nut combo as a complex system that is simplified by separation.


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