# Balancing a Ball in Air

Easy
Have you ever seen a ball suspended in a stream of air? It's a dramatic sight! When you try to pull the ball out of the airstream, you can feel a force pulling it back in. This experiment shows one of the forces that give airplanes lift.

## Hypothesis

The hypothesis is that the air flowing upward hits the bottom of the ball and slows down, generating a region of higher pressure that holds the ball up against the pull of gravity.

## Method & Materials

You will need a blower, a spherical balloon or table tennis ball, and tissue paper. You will balance the ball above the airstream, pull it slowly out of the flow, and tilt the airstream to one side.
You will need a hair dryer, a balloon or table tennis ball, and tissue paper.

## Results

The experiment shows that when the ball is suspended in the airstream, the air flowing upward hits the bottom of the ball and slows down, generating a region of higher pressure. This high-pressure region of air under the ball holds the ball up against the pull of gravity. When you pull the ball partially out of the airstream, the air flows around the curve of the ball that is nearest the center of the airstream, creating an inward force on the ball.

## Why do this project?

This experiment is interesting and unique because it demonstrates the Bernoulli principle, which explains why air flowing over a surface in an arc exerts less pressure on that surface. It also shows how air follows the surface of a sphere and why air pressure on the ball decreases, allowing the normal atmospheric pressure of the calm air on the other side of the ball to push the ball back into the airstream.

## Also Consider

Experiment variations to consider include using a vacuum cleaner instead of a blower, and using a light-weight vinyl beach ball instead of a balloon or table tennis ball. Another variation is to move the blower and the ball toward a wall (try the corner of a room) and observe the great increase in height of the suspended ball.

## Full project details

You can find additional information and details for this science fair project here. Have fun exploring!