Air Pressure

The air we breathe is actually a gas made up of tiny particles constantly flying around and bumping into one another! Here is Jared Goldberg, who studies the physics of stars, discussing air in static and dynamic situations.

Did you know that the air is always pushing on you? We call this air pressure. It may not feel like the air is pushing on you, because we are used to it. What if we were able to take all of the air out of the room, would it feel different?

In the first video, Jared introduces the vacuum pump, which sucks all the air out of the jar. It is easy to lift the jar when the vacuum is off, because the air pressure from inside the jar is equal and opposite the pressure from outside. But when all the air is evacuated, or sucked out through the vacuum pump, he is unable to lift the jar! This shows how strong the 14 pounds per square inch of air pressure from the outside is when there is no air inside the jar.

In the second video, Jared puts a balloon inside a vacuum chamber. The balloon is tied off so it contains a small amount of air inside. When he turns on the vacuum, the vacuum removes all the air pressure outside the balloon (as if it were in Outer Space). You can see the balloon expand in real time! This is because the air particles inside the balloon are bouncing against the balloon wall, without any air pressure from the outside.

In the third video, Jared uses a marshmallow (instead of the balloon) inside the vacuum chamber. Just like the balloon, the marshmallow gets bigger when Jared turns on the vacuum. The air in pockets inside the marshmallow presses on the walls of the marshmallow, so it expands. There is less air pressure on the outside of the marshmallow than inside, so the inside air pushes its way out very easily, making the marshmallow grow.

Unlike the balloon, air can escape through tears in the surface of the marshmallow. Once enough air has escaped into the vacuum, the marshmallow starts to get smaller again. When the vacuum is turned off, the marshmallow collapses as there’s no air remaining inside!

In another demonstration, we learned that Sound waves are vibrations moving through the air. But what happens if there is no air?

In this fourth video, Jared puts a ringing bell inside the vacuum chamber. When air is removed from the chamber, the sound stops as there is no medium for sound waves to travel! This is why there is no sound in Outer Space.

So far we have considered air pressure in static situations, where there is no overall air flow even as individual particles are bouncing around. Now, Jared introduces a Leafblower to discuss dynamic situations where the air is moving.

Moving air can create areas of higher and lower pressure. When Jared turns on the Leafblower, the moving air flows around the racketball. Here the moving air creates an equilibrium where the racketball is held in place, even as Jared rotates the Leafblower!

Finally, Jared adds a funnel to the end of the Leafblower. With the funnel in place, the moving air actually sucks the racketball into the Leafblower! The air moving outside the funnel creates air pressure, which pulls air into the funnel.