[TheForge] The physics of a fire piston

[xlch58 at swbell.net]

Newtonian physics, and the first law of thermodynamics.   It is an 
adiabtic or approximately adiabatic process.

Charles

Bruce Freeman wrote:

>I'm not following this discussion.
>
>The ideal gas law is PV=nRT
>
>where P=absolute pressure, V=gas volume, n=amount of gas (in
>gram-molecular weight, aka "moles"), R=the gas constant (e.g., 0.082
>liter-atmospheres/mole-degreeK), and T is degrees Kelvin.
>
>However Boyle's law states that P1 x V1 = P2 x V2.   I.e., PV is
>constant with changes of volume.
>
>Now if Boyle's law holds, then a fire piston would produce no
>temperature change at all.  What's going on in a fire piston is not
>encapsulated by the ideal gas law. 
>
>So what's REALLY going on has little to do with the ideal gas law and
>instead relates to conservation of energy.  I.e., we do all that work
>shoving down on the piston, and that work is expressed as heat.  The
>trick is to convert mechanical work to heat and to localize that heat at
>the tinder.  
>
>A fire drill is one way of doing that.  A fire piston is another. 
>Beating on a cold piece of steel between a hammer and anvil is a third. 
>Actually, flint and steel is a forth, but this is less obvious because
>what's going on there is that the steel is the primary tinder as well as
>the object upon which the flint does work.
>
>In the case of a fire piston, we have one more advantage - the oxygen
>pressure goes up, making the tinder more likely to combust.
>
>Bottom line:  Come up with a "fire piston" that you can hit with a big
>hammer, and it should be even more effective.
>
>Bruce
>NJ
>  
>