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Expanding Gas: Boyle's Law

How does a CO₂ cartridge propel a car down the track? The answer has to do with Boyle’s Law.

Volume and Pressure
In a confined container, the volume of a gas is inversely proportional to the pressure that is applied when the temperature is constant. Stated another way, if you double the pressure, you reduce the volume by half.
This is exactly the case with CO₂ cartridges. At the factory, they are filled with pressurized carbon dioxide gas and then sealed. The CO₂ is confined to a small container; the volume of the gas would be much greater if it were released into the air. The large volume of CO₂ can fit inside the small cartridge because of the pressure that has been applied to it.

Atmospheric Pressure
The air around us is actually under pressure as well. Atmospheric pressure is 14.7 pounds per square inch at sea level. Imagine a one-inch cube of air. Now imagine a stack of one-inch air cubes that reaches from the ground all the way to the edge of the Earth’s atmosphere. That stack of air cubes actually weighs 14.7 pounds.

The pressure inside a CO₂ cartridge is far greater than atmospheric pressure. That’s why the gas escapes so rapidly when the cartridge is punctured. The gas continues escaping until the pressure inside the cartridge equals the atmospheric pressure outside the cartridge.