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Unlike the biplane that inspired Amelia Earhart to become a pilot, modern jets do not have propellers. How does a jet move through the air? By Action and Reaction. When a jet takes off, hot gasses shoot out of the back of the plane. That’s the Action part. The plane is pushed in the opposite direction and that’s the Reaction part. As long as those hot gasses are blasting out toward the back of the plane, the jet plane will shoot forward.

The hot gasses are creating Thrust. Thrust is the powerful Action that causes the forward movement or Reaction. You can recreate the thrust that moves a plane forward with this fun experiment.

• A door with a doorknob
• String, a minimum of 6-15 feet long.(longer is better)
• A straw
• A chair
• A balloon
• Some tape
• A friend or parent

1. Tie one end of the string to the doorknob.
2. Put the other end of the string through the straw.
3. Stretch the string as far as it will go and place the chair there.
4. Tie the end of the string to the chair.
5. Blow up the balloon and hold the end closed.
6. Ask your friend to place a strip of tape over the straw and onto the balloon so that the balloon hangs under the straw.
7. Let go of the balloon!

• What happened to the balloon and the straw?
• What do you think would happen if you blew the balloon up more?
• Or blew it up less? Try it and find out!

So what really is going on here?

By blowing up the balloon, you are crowding a lot of air into a small space and that creates air pressure. When you let go of the balloon, all the air rushes out, creating thrust and pushing the balloon forward. Since the balloon was taped to the straw, it also pushed the straw along the string, the same way a jet engine pushes a plane forward!