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We say kinetic of molecules as a function of temperature from the equipartition theorem. This means that more is the velocity or mass of the body , more the is the temperature.

My Q is why does increased motion or mass of molecules contribute to heat , increased temperature ?

From this. Is it also possible to say that when velocity of molecules = 0. Then , temperature is at its coldest measure ? Since even at -20K or so. There must be some speed of the molecules where I can say that they are just slow.

I kind of also feel fire and ice also confuse with how they can be compared here ?

To conclude. All these few Q are a subtopic of my major Q i.e why does increased motion or mass of molecules contribute to heat , increased temperature.

S.M.T
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    Hi Srijan, please read once more your post and try to narrow down your questions (I can count at least four direct questions - which admittedly are related somehow), and try -if possible- to ask one structured question. This process will also help you clear your thoughts and improve your understanding. `A problem well stated is a problem half-solved` Charles Kettering. – NMech Jun 14 '21 at 09:08
  • @NMech Sure. Wonderful quote – S.M.T Jun 14 '21 at 09:24
  • @NMech How is it now ? – S.M.T Jun 14 '21 at 09:30
  • better but still there are things like: *Then , we also mean to say that as molecules move here and there . Temperature of a body increases.*. To my mind, what you are trying to write is *Then, we also mean to say that as molecules move here and there, the temperature of body increases.*. I can't be sure that's on your mind though. You are making excessive (and incorrect IMHO) use of full stops, and end up confusing the reader. – NMech Jun 14 '21 at 09:34
  • @NMech Ok. I’ll make it more simpler then. – S.M.T Jun 14 '21 at 09:34
  • Don't make it on my account. Do it if you feel it will improve the readability of your post. English is not my native language, so I am hardly an expert. – NMech Jun 14 '21 at 09:36
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    @NMech Ok. It should be understandable for everyone. Accepting feedback is also one of the most important things in life.My family tells me. – S.M.T Jun 14 '21 at 09:41
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    (If you permit me another "life coaching" comment:) *Equally important is to be able to assess which feedback is helpful and which is not*. As an engineer it is something you will surely need. – NMech Jun 14 '21 at 09:46
  • @NMech Of course . Thanks. – S.M.T Jun 14 '21 at 09:52

1 Answers1

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IMHO you are still confusing heat with temperature (despite the answer to this question or this ).

My Q is why does increased motion or mass of molecules contribute to heat , increased temperature.

I will try to answer in a way that address that fundamental difference.

Consider 1 kg of water in a well insulated vessel which is travelling with 10[m/s]. However the temperature of the water is:

  • 200 Kelvin: So water is in solid (ice) state
  • 300 Kelvin (approx 27 $^oC$): so its mostly in liquid state
  • 400 Kelvin (approx 127 $^oC$): so its mostly in gaseous state.

The speed of the vessel does not have an immediate effect on the temperature.

It does however contribute to the overall energy of the system (this is to reply to your question) (NOTE: please edit your punctuation in the question).

Is it also possible to say that when velocity of molecules = 0. Then , temperature is at its coldest measure?

Regarding the part of your question:

Since even at -20K or so. There must be some speed of the molecules where I can say that they are just slow.

There can be no negative temperatures. Even, if you could reach absolute Zero, then the energy of the system would never be entirely zero due to quantum effects ( I've had a theoretical Laser physicist try to explain it to me, but my brain shut down after hearing a few times the word quantum).

Update for comment

If I put ice on my skin. Is it that the molecules of ice are trying to slow down the velocity of the molecules of my skin.

When you put ice on your skin, the molecules of water don't have much internal energy, so they are barely moving in the lattice. When you put them in contact with your skin (which has a lot of water molecules at higher temperature), what happens is that they exchange heat .

I am not an expect on the exact mechanism that heat is exchanged, but I tend to think about it the classical sense of two balls of water molecules hitting each other. The result is that energy is transferred in the impact and some energy is imparted (statistically from the fast moving molecule to the slow).

Because of this exchange, the hotter becomes cooler, and the cold becomes warmer (until eventually the exchange statistically is the same).

UPDATE 2: Fan example

Another example , AC or fan. Do they try to reduce the velocity of molecules of your body.

The reason you get cooling with the fan against your skin, is that the fan pushes to your skin air which is slightly cooler than your temperature.

The reason why the exchange is more severe, is that the more cooler molecules will hit your body and exchange heat in a unit of time (see forced convection.

The fan by itself will actually increase the temperature of the air and the room.

NMech
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  • Coldest temperature was -126 Fahrenheit at Vostok station in Antarctica. How is this temp -ve ? – S.M.T Jun 14 '21 at 10:12
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    [-126 Fahrenheit is 185.372K](https://www.google.com/search?q=-126+Fahrenheit+in+K&sxsrf=ALeKk01DsBhTBnw9M6_BmzhPqaW7uspQYQ%3A1623665607410&ei=xyvHYM_IGMK5kwXtkpaQCw&oq=-126+Fahrenheit+in+K&gs_lcp=Cgdnd3Mtd2l6EANQpiJYpiJg4SNoAXAAeACAAVuIAaoBkgEBMpgBAKABAaoBB2d3cy13aXrAAQE&sclient=gws-wiz&ved=0ahUKEwiPyI3e8ZbxAhXC3KQKHW2JBbIQ4dUDCA4&uact=5) – NMech Jun 14 '21 at 10:14
  • And btw what is **-ve**? – NMech Jun 14 '21 at 10:15
  • Ok. Did you get the feel of my Q when I wrote how is Sth like moving here and there or velocity is same as temperature ? Did you ever feel it be weird ? – S.M.T Jun 14 '21 at 10:15
  • Negative it means – S.M.T Jun 14 '21 at 10:16
  • Like for example. If I put ice on my skin. Is it that the molecules of ice are trying to slow down the velocity of the molecules of my skin. – S.M.T Jun 14 '21 at 10:17
  • In your previous comment *when I wrote how is **Sth** like moving*, what does that **Sth** mean? – NMech Jun 14 '21 at 10:17
  • Sth = molecules. – S.M.T Jun 14 '21 at 10:17
  • I wouldn’t try to do the same with fire . But yes If take a hot body. Does it try to increase the velocity of my skin molecules. Another example , AC or fan. Do they try to reduce the velocity of molecules of your body. – S.M.T Jun 14 '21 at 10:19
  • In your comment. When your wrote two balls of water molecules hit each. They exchange heat. How ? I think it is because one tries to reduce the kinetic merger of velocity of the other molecule ? In turn , the velocity of the molecule itself also reduces. Third law. What you wrote is exact.@NMech – S.M.T Jun 14 '21 at 10:27
  • Assume you have two balls, one standing and one moving. If you hit the standing ball with the moving then, energy is imparted. (Was there a question if your previous comment? *They exchange heat. How ?*) – NMech Jun 14 '21 at 10:30
  • Exchange of heat is nothing but molecules exchanging speed. In turn , one reduces and other increase. In end , they reach equilibrium – S.M.T Jun 14 '21 at 10:30
  • Yes. Right. Also , energy is imparted to both the balls. How I think for this is like imagine one ball is heavy and stranding still. Other is lighter but very fast. Now , still. Two things will happen. The lighter ball will bounce back and the heavier ball may move a bit ahead. So , energy is imparted to both the bodies. – S.M.T Jun 14 '21 at 10:32
  • I’m sorry if my autocorrect makes some words wrong in text. – S.M.T Jun 14 '21 at 10:33
  • All I’m saying is when you wrote exchange of heat , i got a Q in mind that “ How is that heat exchange ? “. For that , I think it is because of exchange of energy between the two molecules. Where velocity or speed plays the part of reducing and increasing speed. – S.M.T Jun 14 '21 at 10:37
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    @SrijanM.T to elaborate on the 0 velocity comment, you cannot have 0 velocity of an atom because of the Heisenberg uncertainty principle, quantum effects... The principle says you can never know the exact position and velocity of a particle. If you were able to measure a particle with 0 velocity you would violate the uncertainty principle. – Feynman137 Jun 14 '21 at 23:11