Entropy makes water run uphill in trees

Entropy makes water run uphill in trees - ROBERT C PLUMB W...

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chemical principles ROBERT C. PLUMB Worcaler Polyteh~~ lnllilula Worcesler. Massach~~th 01609 exemplified Tire Inflation Thermodynamics lllustroting the first low of thermodynomics, ond thermodynamics of gores Suggestion by John J. Connors, Cranston (R. I.) West High School The backyard of your home can serve as a teaching laboratory where the children, and perhaps your spouse, can be enlightened on the subject of thermo- dynamics. Some interesting thermal effects are easily observable when youinflate a bicycle tire. Pump up an English style tire to 60 psi with a hand pump and feel the valve stem. It gets noticeably warm (AT = 22'F in our experiments). Is this due to "friction"? You can test the "friction" hypothesis, and other hypotheses such as that it is due to the Joule- Thompson effect, by another experiment. Observe the temperature rise of the valve stem when the tire is inflated at a compressor at the neighborhood gas station. Usually the valve does not get hot when inflated from a compressor (AT < 1°F in our experi- ments), but it does get hot when inflated with a hand pump. Thus it can't be "friction" since the air flow is about the same in the two cases. Then what causes the effect? The work which you do with a hand pump in com- pressing the gas raises its internal energy. The process is sufficiently rapid as to be approximately adiabatic; that is, no thermal energy transfer takes place and q = 0.
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This note was uploaded on 02/12/2010 for the course BIOMEDE 221 taught by Professor Michaelmayer during the Fall '07 term at University of Michigan.

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Entropy makes water run uphill in trees - ROBERT C PLUMB W...

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