The exit velocity of a compressed air cannon

TL;DR

This paper investigates the exit velocity of a compressed air cannon, comparing different gas expansion models, and introduces a new model based on airflow through the valve that better matches experimental data.

Contribution

The paper presents a new flow-based model for predicting projectile velocity in air cannons, resolving discrepancies between adiabatic and isothermal assumptions.

Findings

Neither adiabatic nor isothermal models accurately predict exit velocity.

The new flow-based model aligns closely with experimental results.

The study enhances understanding of gas expansion dynamics in air cannons.

Abstract

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 energy 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. We built an air cannon that utilized a diaphragm valve to release our pressurized gas and found that neither model accurately predicted the exit velocity of our projectile. We present a new model, based on the flow of air through the valve, that is in much better agreement with our data.