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| Really Boring Post | |
| Posted By: SiliconDream <querl@uclink4.berkeley.edu> | Date: 11/15/99 1:21 a.m. |
In Response To: Re: Powers up the Trademarked Weapon™ (Mage) > No, pressure makes heat... I JUST explained it.when under
But your explanation is wrong. When you compress a system you provide it with energy. (You have to expend energy to overcome the system's internal pressure, which is trying to expand it.) This energy shows up as a rise in the system's temperature. So the energy is provided by the compressing force, and absorbed by the compressed substance, the internal pressure of which goes up as a result. It may then be radiated/conducted out of the pressurized substance into the surrounding medium, but that doesn't mean the energy came from the interior in the first place. Take the example of a gas in a box. Its temperature is a measure of the average momentum of its molecules; its heat is the total kinetic energy of its molecules. It exerts pressure on the walls of the box because its molecules are constantly ricocheting off them, pushing them outwards. Now you compress the gas; that is, you push the walls of the box inward. Every time a gas molecule bounces off a box wall, it gains a bit of energy from the wall's motion, just as a tennis ball picks up speed from the motion of the racket which hits it. The bounce also slows down the collapse of the wall (by conservation of energy and momentum) so that you have to push a little bit harder (expend more energy) to keep the wall moving. In this way energy flows from the compression mechanism (your muscles in this case) to the compressed gas. Since heat is the same as total kinetic energy, the total heat stored in the gas increases. And because faster-moving molecules hit the walls of the box harder, the pressure the gas exerts on the box increases. Again, the pressure is generated by the kinetic energy in the gas (and its density), which is drawn from the compression mechanism. Mark's already explained the other compression model (for compression without "walls"), so I won't get into that. Remember: nothing sucks but everything blows! --SiliconDream | |
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