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# Re: [Phys-l] Temp & Energy density

Thanks John.

If this results in an increased P wouldn't the accompanying decrease in V (since the piston snuck down a bit when none of the gas particles were looking) result in an increased T? Or is this using pv=nrt when it doesn't apply?
A material science prof and a physicist (both working separately on low pressure environments: 1 on material characterization the other on thin film deposition) both teased me with the piston question. I don't know if they were on cahoots or not.
My response was no temp change due to no real work. They seemed (at the time) to find this acceptable. I've just been approached with the energy density arguement. I'm trying to resolve the two conceptions.

I appreciate the help. Thanks fir your responses and patience.

Sent from my iPod so I can blame Apple for my typos.

Paul Lulai
St. Anthony Village Senior High
Http://prettygoodphysics.wikispaces.com
US First RoboHuskie Team 2574

On Aug 3, 2009, at 11:18 PM, "John Mallinckrodt" <ajm@csupomona.edu> wrote:

Paul Lulai wrote:

Larger energy density implies increase in temp.

Simply not so. Others seem not to have directly addressed the
central misconception here so allow me.

Example: For a monatomic ideal gas at equilibrium

PV = Nkt = (2/3)U

thus

energy density = U/V = (3/2)P

That is, energy density is directly proportional to equilibrium
pressure and has no direct connection to temperature.

John Mallinckrodt
Cal Poly Pomona
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