# Ping-Pong Levitation

## Learning Objectives

Through observation, students will discover that flight occurs when the characteristics of structures take advantage of certain properties of air.

## Associated Curriculum Topic

Properties of air and principles of flight

## Materials

• A hair dryer with a cold setting
• 2L bottle or water bottle (judge whichever is closer to the size of the hair dryer nozzle)
• Ping pong ball
• Balloon (blow the balloon up to a size that is larger than the ping pong ball, however small enough that it remains as round as possible)
• empty toilet paper tube (optional)
• Scissors
• Duct Tape

## Introduction/Motivation

This activity demonstrates levitation by using the properties of air. With the use of a hair dryer, with a 2L bottle nozzle attached to it, the air flowing from the hair dryer will be concentrated into a narrow stream. When you place a ping pong ball in the air stream above the hair dryer, it levitates! This is an example of what's called Bernoulli's principle. Bernoulli, a Swiss scientist who wanted to find out how these things work, discovered this effect more than 250 years ago. He found out that the faster air slips past the surface of something, the less the air pushes on that surface (and so the lower its pressure). When you place the ball in the stream of air created by the hair dryer, you force the air to flow around the ball and create an area of lower pressure. The still air surrounding the air stream has more pressure and pushes the ball to keep it snuggled in the stream. When you place the empty toilet paper tube into the air stream, the air is funneled into a smaller area, making air move even faster. The pressure in the tube becomes even lower than that of the air surrounding the ball, and the ball is sucked up into the tube.

## Procedure

### Pre-Activity preparations

• Cut the 2L bottle or water bottle at the point where the spout is at a diameter which would fit onto the nozzle of the hair dryer; secure to hair dryer with duct tape.

### Procedure with students

• With the hair dryer on its cold setting, direct the air flow upwards and place the ping pong ball into the stream of air. The ping pong ball should float approximately 10 cm above the spout.
• Try walking slowly, tilting or jiggling the hair dryer.
• Now try slowly lowering an empty toilet paper tube over the ball.
• Place the balloon above the floating ping pong ball and watch it float above the ping pong ball.

### Trouble shooting

• Ping pong ball will not float: Try turning the hair dryer onto a warmer setting, or one which has a higher velocity of air. Also check to make sure that the air is coming out of the spout and not sneaking out from the duct tape regions.

## Investigating Questions

• What is gravity?
• What does the word ‘levitation’ mean? How is it related to gravity?
• What happens when the hair dryer is tilted or jiggled? Why?
• What happens when the toilet paper tube is above the ball? Why?
• Why do the larger objects need to go above the smaller objects?