Atmospheric Pressure and Bernoulli

AIR PRESSUREStudent in bubble

Bottle Collapse

A 3-liter bottle is easily crushed by atmospheric pressure when connected to a vacuum pump. Free one gallon metal cans are hard to find these days.  

Magdeburg Hemispheres

The five inch diameter plates would require a force of nearly 300 pounds to separate them if it were a perfect vacuum and seal, in fact about half that is all that's needed.

Burning Paper in a Measuring Cylinder

Drop a piece of burning paper into a measuring cylinder and then cover the open end with your palm, or other part of your anatomy. I've used the top of my bald head and my belly. The flame extinguishes once the oxygen is used up. When the gases in the cylinder cool, the pressure inside drops, sticking the cylinder to your body. It's a cheap demonstration of atmospheric pressure, but don't leave the cylinder on too long or you'll have a vivid demonstration of the pressure within blood vessels.

Guinea & Feather Tube

In this classic demonstration a feather and a coin are dropped in an evacuated tube. As objects at the same location have the same weight to mass ratio, hence they have the same acceleration in a vacuum.


I'm not sure what the Physics is here, but it's a wonderful demonstration of something. (Okay, it could lead into surface tension, thin film interference, evaporation rates, minimum area topology, etc. I just like bubbles.) A paddling  pool with a small step stool placed in the middle may be substituted for the custom made fiberglass tub, but be careful when stepping on or off. Use a hula hoop for the bubble hoop, a piece of broom handle is fastened to the hoop with a single screw and then electrical tape is wrapped over that section to cover any sharp edges on the screw. I'm told that it helps to wrap the hula hoop in gauze, I can believe that.
Bubble Recipe:
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Bernoulli Effect Demonstrations

Use a shop vac to support a 4 inch diameter foam ball in the air. Smooth surface balls work best. Large balloons of the 'punch ball' variety also work well in a room with a high ceiling. The faster a fluid moves, the lower it's pressure gets to be, all else being equal. The angle of attack is just as important for plane wings, as regards lift and the seams on the base ball drag the air around making curve balls possible.

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