## Atmospheric Pressure and Bernoulli

### AIR PRESSURE

• Soda bottle collapse
• Magdeburg hemispheres
• Stick cylinder to hand
• Guinea & feather tube
• Bubbles - Receipe
• Bernoulli effect: balls in a stream of air.
• Bernoulli effect: funnel & balls
• Curve balls
• Large glider

### 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.

### Bubbles

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:
• 1 cup Joy or Dawn dish washing liquid
• 3 - 4 tablespoons glycerine (optional, obtain from pharmacy)
• 10 cup clean, cold water (up to 50% more on a dry day)