Bernoulli's Dancing Balloons

This is one of my favorite experiments for all ages. The kids at Khalsa-Camden did this last Fall and had a ball (literally). It is a wonderful experiment to show the relationship (that the famous scientist Bernoulli explained between) between velocity and pressure, using balloons, fans, and beach balls. This experiment is best done outside on a still day with no wind. Here's what you need to get started:

• a floor fan that can pivot vertically to horizontally, so that it can be positioned to blow upward (while leaving some airspace under the fan).
• balloons (already blown up).
• beach balls of all sizes.

Have your kids hypothesize about what they think will happen to the balloons if you turn the fan on (blowing upward) and let go of the balloons over the blowing air. Do the same with the beach balls.

What you should find is that once you let go of the balloons or beach balls, they will travel upwards in the air stream. Most kids will expect the balloons or balls to fly everywhere and for the them to fall back down to the ground. However, once the balloons and balls travel high enough in the air stream, they will appear to "dance" in the air and not fall down or fly outward away from the air stream. The reason they stay where they are is because the faster air blowing upward from the fan is creating an area of lower pressure than the surrounding air. The balloons and balls are "trapped" in the low-pressure area and will only come down when the fan is turned off or if a gusty wind pushing them along.

The kids will have the most fun when you place several balloons over the fan rather than just one. Try it at home and let me know if it worked for you!