The use of compressed air cannons in an undergraduate lab provides a way to illustrate the
cooperation of diverse physics concepts, such as conservation of momentum, the work-kinetic en-
ergy theorem, expansion of gas, air drag, and elementary Newtonian mechanics. However, recent
proposals have disagreed as to whether the expansion of the gas in the cannon should be modeled
as an adiabatic or an isothermal process.
In conclusion, we have shown that both the adiabatic and isothermal expansion models
are not consistent with our data. A gas flow model that accounts for the valve is in much
better agreement with the data. This is because the assumption of both the adiabatic and
isothermal models that the air pressure in the reservoir is the same as the pressure in the
barrel is dicult to meet given the necessity of using a valve to pressurize the reservoir. We
now have a way to predict exit velocity as a function of initial tank pressure, which will be
useful in the development of future undergraduate labs utilizing compressed air cannons.
Check it out here.