You’ll need

  • A hair dryer
  • A ping-pong ball

What to do

  1. Turn on your hair dryer to the highest fan speed. Select the cool setting if you have one.
  2. Point the hair dryer straight up and place the ping-pong ball within the flow of air. Gently release the ball in the middle of the airstream.
  3. If you have placed the ball in the right spot, it should float in place. Test your skills and see how far you can tilt the hair dryer to the side before you lose the ping-pong ball.

Questions to ask

Try using a balloon instead of a ping-pong ball. Does it work as well? How big can you blow up the balloon before it stops levitating? What happens if you use balloons that are not round?

If you can find the things you need, try using a bigger ball, such as a beach ball, and a bigger air source, such as a leaf blower.

What's happening

The ping-pong ball will fly up with the air from the hair dryer until it reaches a point of balance. This is where the force of gravity (which pushes the ping-pong ball down) is equal to the force of the air (which is pushing the ping-pong ball up).

But why doesn’t the ball go flying off the stream of air?

Because of something called the Coanda effect. This is a phenomenon whereby moving fluids or airstreams stick to surfaces they are moving past.

As the air flows past the ping-pong ball, it passes along all sides of the ball, and pushes evenly on all sides. This is what keeps the ball in the airstream.

If you tip the hair dryer on a slight angle, the Coanda effect continues to hold the ball in the airstream. But if you tip the hair dryer so far that the force of gravity outweighs the force of the air, the ball falls to the ground.