Does kinetic energy transform into heat at a microscopic level?

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Discussion Overview

The discussion revolves around the transformation of kinetic energy into heat at a microscopic level, particularly in the context of a hypothetical scenario involving a ball of gasoline and oxygen. Participants explore the distinctions between different forms of kinetic energy and their implications for thermal energy and combustion, touching on concepts from both classical and statistical mechanics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant proposes a scenario where a ball of gasoline in a ball of oxygen accelerates to relativistic speeds, questioning whether it would explode from kinetic energy.
  • Another participant distinguishes between linear kinetic energy of the center of mass and thermal energy, suggesting that increasing linear kinetic energy does not necessarily lead to more frequent molecular collisions.
  • A participant emphasizes that the question can be analyzed using both special relativity and Newtonian mechanics, leading to the same conclusions.
  • JesseM raises a concern about the distinction between translational kinetic energy and internal degrees of freedom, noting that the average kinetic energy discussed does not account for molecular rotation and vibration.
  • Some participants express skepticism about whether kinetic energy can transform into heat, particularly in the context of high-energy particles in colliders.
  • There is a discussion about the implications of different inertial frames on the perception of heat and energy transfer, with a participant asserting that linear kinetic energy does not convert to heat when viewed from different frames.
  • Participants reference statistical mechanics to clarify that heat energy is associated with the random kinetic energy of particles, which includes various degrees of freedom.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between kinetic energy and heat, with some agreeing on the definitions of energy forms while others remain skeptical about the transformation of kinetic energy into heat. The discussion does not reach a consensus on these points.

Contextual Notes

There are unresolved questions regarding the assumptions made about kinetic energy and heat transformation, as well as the definitions of energy forms in different frames of reference. The discussion also highlights the complexity of relating macroscopic observations to microscopic behaviors.

completenoob
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I had an odd thought. Suppose I have a ball of gasoline inside a ball of O2 in free space. The ball and I start in the same inertial frame with respect to some planet. The ball starts accelerating. The ball reaches the kinetic energy enough for the combustion of gasoline[I think this will depend on the mass of gas present, but suppose that it is really high and such that the velocity is say 95% the speed of light]. From my frame of reference the ball would explode right?
 
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No, you have to distinguish between linear kinetic energy of the center of mass and thermal energy which is due to the random motion of the molecules in all different directions. Increasing the linear kinetic energy won't cause the molecules in the ball to collide with one another more frequently, for example. All inertial frames make the same predictions about local physical events, so you can't have a situation where one frame predicts it'll explode and another doesn't.
 
And note that this has absolutely nothing to do with SR. You could write down exactly the same question in Newtonian mechanics and it would have exactly the same answer.
 
JesseM: Is your explanation the same as here:

It is important to note that the average kinetic energy used here is limited to the translational kinetic energy of the molecules. That is, they are treated as point masses and no account is made of internal degrees of freedom such as molecular rotation and vibration.

http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/kintem.html#c1

Kudo's if so!
 
Naty1 said:
JesseM: Is your explanation the same as here:
http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/kintem.html#c1

Kudo's if so!
The distinction they're making between translational kinetic energy and "internal degrees of freedom such as molecular rotation and vibration" isn't the same as the distinction I was talking about, if that's what you mean--on that page they're still talking about translational kinetic energy of molecules in random directions, which does make the substance hotter (and gasoline closer to exploding) the greater it is, whereas I was talking about the kinetic energy of the system's center of mass, in other words the extent to which the average velocity of all the molecules is pointing in a single direction. On that page I think they're assuming that we're using the rest frame of the center of mass to define the average kinetic energy...
 
JesseM..yes that's what I meant...
...so I'm unsure what their answer means...I have never considered whether KE transforms to heat in any way...never heard such a thing...whether high energy particles in colliders, for example, are "hot"...it sounds like from their description "yes" but I'm skeptical...

In other threads length contraction as explained (by DrGreg I think) does NOT result in compression forces and hence no heating...thermodynamics scares me...
 
Naty1 said:
JesseM..yes that's what I meant...
...so I'm unsure what their answer means...I have never considered whether KE transforms to heat in any way...never heard such a thing...whether high energy particles in colliders, for example, are "hot"...it sounds like from their description "yes" but I'm skeptical...
Linear kinetic energy of a system's center of mass doesn't transfer to heat, since you can just transform into a different frame where the center of mass of the system is at rest, and different frames can't disagree about local physical questions like whether a ball of gasoline is hot enough to explode. Their point is that at a microscopic level, heat energy is really just due to the random kinetic energy of all the particles making up the system, which have velocities in all different directions--this is a standard idea in statistical mechanics, where temperature for a system at equilibrium can be defined in terms of the average energy per "degree of freedom" (which includes each molecule's freedom to move in any of the three spatial directions, along with rotational and vibrational freedom). I think it's usually assumed in statistical mechanics that we're using the rest frame of the system's center of mass, though.
 

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