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Irrelevancy Of Friction?


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#1 hazelm

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Posted 23 October 2019 - 07:35 AM

Today Delancey Place is posting a review of Seven Brief Lessons on Physics by Carlo Rovelli.  The topic is "heat", how it is produced from friction and when it is relevant - showing past and future but not relevant in such as the motion of planets.  Then, he says it is totally irrelevant in the motion of the planets where we see no past and future. 

 

Hoping I am reading this right, my question is why is there no friction to create heat in the motion of the planets?  What about the heat from the sun and the friction created within the sun by motions from the various elements therein which I think heat to different caloric levels?  Doesn't the friction of these elements create  heat that is passed to the planets?

 

That, of course gets to the question of what created the motions that created the friction and why are they different (I think).  But we will skip the "Where is the beginning?" bit.  For now, isn't heat from the sun passing to the planets, creating motion of the planets? 

 

The newsletter source is (email inbox link redacted)

 

If past experience is any promise, some of you may not be able to access this  by way of that link.  If not, perhaps you can find it at <<delanceyplace.com>> and a search for Seven Brief Lessons on Physics by Carlo Rovelli, subtopic:  heat.

 

Thank you for thoughts on my question.


Edited by GAHD, 25 October 2019 - 07:43 AM.
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#2 exchemist

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Posted 23 October 2019 - 10:28 AM

Today Delancey Place is posting a review of Seven Brief Lessons on Physics by Carlo Rovelli. The topic is "heat", how it is produced from friction and when it is relevant - showing past and future but not relevant in such as the motion of planets. Then, he says it is totally irrelevant in the motion of the planets where we see no past and future.

Hoping I am reading this right, my question is why is there no friction to create heat in the motion of the planets? What about the heat from the sun and the friction created within the sun by motions from the various elements therein which I think heat to different caloric levels? Doesn't the friction of these elements create heat that is passed to the planets?

That, of course gets to the question of what created the motions that created the friction and why are they different (I think). But we will skip the "Where is the beginning?" bit. For now, isn't heat from the sun passing to the planets, creating motion of the planets?

The newsletter source is (email inbox link redacted)

If past experience is any promise, some of you may not be able to access this by way of that link. If not, perhaps you can find it at <<delanceyplace.com>> and a search for Seven Brief Lessons on Physics by Carlo Rovelli, subtopic: heat.

Thank you for thoughts on my question.

I can’t access it but I imagine he is just saying the planets move in a vacuum so there is no frictional heating due to their motion. I am guessing but I imagine his slightly contrived point is that in a thermodynamic system that is reversible, entropy does not increase. Some people call entropy the arrow of time, because irreversible processes always involve an increase in entropy.

However he is strictly speaking wrong because there are such things as tidal effects, by which planets cause motions within the sun which lead to extra heating, just as the moon causes the ocean tides and the flow of water causes a bit of heating. :)


Edited by GAHD, 25 October 2019 - 07:44 AM.
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#3 hazelm

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Posted 23 October 2019 - 01:04 PM

I can’t access it but I imagine he is just saying the planets move in a vacuum so there is no frictional heating due to their motion. I am guessing but I imagine his slightly contrived point is that in a thermodynamic system that is reversible, entropy does not increase. Some people call entropy the arrow of time, because irreversible processes always involve an increase in entropy.

However he is strictly speaking wrong because there are such things as tidal effects, by which planets cause motions within the sun which lead to extra heating, just as the moon causes the ocean tides and the flow of water causes a bit of heating. :)

You are probably right but I'd argue it because our solar system planets also move in a vacuum.  Are we getting any frictional heating?  But then you said due to their motion.  Maybe I got that backward.  Frictional heating causes motion.  Is it worth saying that it depends on the planets being hit?  In our own, for example, the outer planets would get little or almost none. Our two inner planets have been overheated.  and died.  Then there is Earth which is "just right".  Mars and Jupiter were maybe at one time.  Now gravity is continuing the motion-process.  Yes?  Hmmmm?  Would the rocky planets - with all their metals - attract more heat?

 

OK.  I'm not sure where I am going with that.  Best stop before I get lost in space.  But I'll think on it.  Your point about entropy I will have to concentrate on.  Entropy always seems to work backward to me.  (Don't ask. <g>)

 

Thanks again. 



#4 exchemist

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Posted 23 October 2019 - 02:00 PM

You are probably right but I'd argue it because our solar system planets also move in a vacuum.  Are we getting any frictional heating?  But then you said due to their motion.  Maybe I got that backward.  Frictional heating causes motion.  Is it worth saying that it depends on the planets being hit?  In our own, for example, the outer planets would get little or almost none. Our two inner planets have been overheated.  and died.  Then there is Earth which is "just right".  Mars and Jupiter were maybe at one time.  Now gravity is continuing the motion-process.  Yes?  Hmmmm?  Would the rocky planets - with all their metals - attract more heat?
 
OK.  I'm not sure where I am going with that.  Best stop before I get lost in space.  But I'll think on it.  Your point about entropy I will have to concentrate on.  Entropy always seems to work backward to me.  (Don't ask. <g>)
 
Thanks again.

OK Hazel, take it easy. If I ever live to your age I doubt I’ll be up to discussions on science forums at all! :)
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#5 hazelm

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Posted 23 October 2019 - 03:52 PM

OK Hazel, take it easy. If I ever live to your age I doubt I’ll be up to discussions on science forums at all! :)

Thanks.  If I succeed at all, the thanks go to the company I keep.  :spin:



#6 GAHD

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Posted 25 October 2019 - 07:43 AM

First off, you linked to your gmail inbox and all that link will do is try to auto-login anyone who clicks it to that gmail email thread...which only your account has access to. You should use a different link. I've edited it out to protect your account token. Try finding a link that doesn't start with "mail dot stuff"

Strictly speaking the solar system isn't a true vacuum and meteorite strikes should count as friction, but "close enough" is close enough. Like exchem said there's also tidal forces from the various complex barycenters that cause friction as well as magnetic drags from the various planetary dynamo. Io is a probably a good example of both forms of friction there.

Can't really get much of an idea of what's actually being said without actually looking at source but it sounds like some convergence of philosophy?



#7 hazelm

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Posted 25 October 2019 - 01:06 PM

First off, you linked to your gmail inbox and all that link will do is try to auto-login anyone who clicks it to that gmail email thread...which only your account has access to. You should use a different link. I've edited it out to protect your account token. Try finding a link that doesn't start with "mail dot stuff"

Strictly speaking the solar system isn't a true vacuum and meteorite strikes should count as friction, but "close enough" is close enough. Like exchem said there's also tidal forces from the various complex barycenters that cause friction as well as magnetic drags from the various planetary dynamo. Io is a probably a good example of both forms of friction there.

Can't really get much of an idea of what's actually being said without actually looking at source but it sounds like some convergence of philosophy?

Someone else told me that, also, GAHD but I can't figure it out.  Hmmm?  Or maqybe I can.  The review is in my box when I open it.  So, guess that is it.  And I can't copy/paste - copyright laws.  Funny this, though, is that some people do get it.  Whatever.  Guess all I can do is say go to Delancey Place and do a search for that book.  Maybe you have to be signed up for the newsletter.

 

I actually had the book but gave it to a friend.  Maybe I'll get another copy.