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Old Nov 23rd 2009, 01:13 AM   #1
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heat in w.e theorem

i was wondering how work -energy theorem in mechanics incorporate heat? any help will be welcomed with delight.
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Old Nov 24th 2009, 01:27 AM   #2
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There is no heat in mechanics. Heat is a later chapter!Actually i dont think we bring in heat directly except maybe as occurring due to friction etc.
Come to think of it we dont consider sound either during collisions.
Linking heat and work happens in thermodynamics.
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Old Nov 29th 2009, 06:44 AM   #3
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now i am worried about another thing.( this happens to me off and on)
why cannot we create a complete work energy theorem incorporatng all types of energy- electromagnetic, heat, grav and all?
what if i apply kinetic theory of gases to a gas jar in a accelerating train?
can i still conclude RMS velocity=root 3RT/M???

Last edited by r.samanta; Nov 29th 2009 at 07:40 AM.
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Old Nov 29th 2009, 11:04 PM   #4
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Such worries are welcome.

Normally when we invoke the work energy theorem we are in the domain of mechanics. Of course for total enegy accountability, we would have to consider other forms of energy. For example if a charged block is accelerated on a rough surface and collides with a wall with a thud, we would have to consider the energy loss due to heat, sound , radiation of electromagnetic energy (as charge is accelerated) etc. But i think we may find that these losses are small compared to the main values being considered and are hence not taken into account.

As far as the accelerated jar goes, when we consider the gas as a single entity say with a total mass then in mech problems we would have to consider it.

But if we think of it as individual atoms floating around in a container with space in between them, then the motion of the jar does not really affect them,(i.e. does not cause any accelaration of the atoms) except that one wall rushes towards them and the other away.

If we consider the jar to be moving in the +ve x direction, the left wall rushes towards the atoms and the right one away. As always is the case in kinetic theory, half the atoms can be considered to be moving in the -x direction and the other half in the +x direction and hence whatever effects this motion introduces will cancel out on the average.
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