Monday, June 14, 2010

Air Pressure: Straw Fountain

Fill a cup part way with water.

Hold a straw vertically in the water – make sure it’s not touching the bottom of the cup. (You could probably tape the straw to the cup if you’re having a hard time holding on to all of the parts.)

Using another piece of straw, blow across the top of the straw that’s in the water.

What happens:
Water shoots out of the vertical straw.

Normally there’s a whole lot of air molecules stacked up on top of the surface of the water. When you blow across the top of the straw, you’re pushing some of those air molecules out of the way. There are still air molecules pushing on the rest of the water, and with the pressure over the straw reduced, the water is pushed up the straw.

If you're having a hard time getting the water to shoot out of the straw, try some of these tips - they helped me!

1 - Aim the straw you're blowing through slightly up (see picture above).

2 - Use shorter pieces of straw.

3 - Fill the cup with more water.

4 - Practice - it takes a few times to get the technique down.

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