Pressure and Ideal Gas Law

Do you feel that? On your shoulders? That weight? About 1200 lbs. Right now there is about half a ton of air sitting on your shoulders, pressing you down. Before you start thinking that you are a beast and can squat way more than you thought, you have to be aware that we can't really feel this weight, or at least we are used to it. That doesn't mean that its not there. In fact, that weight of air can be used to crush a 55 gallon steel drum.

Not impressed? What if I told you that air could even crush a train? Don't believe me... Go ahead, watch this.... I'll wait.

Air pressure, or the force exerted by a gas trying to expand, can be incredible. We are already pretty familiar with this idea with water pressure. Ever try to swim to the bottom of a pool? This is what is happening to your chest and ears.

The questions remains though: Why does this happen? Or, why don't things get crushed all the time? To answer that we'll need to understand pressure and the ideal gas law. This tells us that there is a relationship between temperature, pressure, and volume. But if that is the case, pressure should be able to do more than just crush things, right? Kaboom.

Here are some specifications for each scenario so we can do some investigation of our own. Assume that each example took place at 1 atmosphere of pressure: 1.01 x 10⁵ pa.

55 Gallon Drum: 23 in diameter, 35 in tall.Assume no interior pressure.

Train Car Dimensions: 6.1 m long, 2.6 m high. Assume no interior pressure.

Hot Water Heater Dimensions: 22 in diameter, 30 in height; Interior Pressure: 2.3 x 10⁶ pa.