Students explore Newton’s Third Law of Motion (“for every action there is an equal and opposite reaction”) by building a hovercraft.

The small hole in the centre of the CD forces air escaping from the balloon downwards. This creates an opposite force upwards which lifts the hovercraft off the ground, explained by Newton’s Third Law of Motion. The CD spreads out this force evenly along the bottom of the hovercraft.

Having a thin layer of air helps also helps the hovercraft move by reducing the amount of friction between the CD and the ground.

### Objectives

• Describe Newton’s Third Law of Motion and its applications.

• Describe the effect of friction on movement.

### Materials

• Per Class:
4 hot glue guns and glue sticks, or duct tape

• Per Student:
CD
sport drink cap (with pop-out nozzle)
balloon

### Key Questions

• When the balloon is released, where will the air go — up, down, or to the sides?
• What would be the opposite and equal reaction, according to Newton’s Third Law of Motion?

### What To Do

Preparation:

1. If using glue guns, set up four hot glue gun stations around the classroom. This ensures that the mess will be contained!

Instructions:

1. Hand out a CD, a sport drink cap, and a balloon to each student.
2. Glue the bottom of the sport drink cap to the shiny side of the CD, making sure that the hole in the cap and CD are aligned. Hold for a few seconds or until the glue is dry.
3. Put the balloon over the top of the sport drink cap.
4. Blow up the balloon through the CD.
5. Pinch or twist the neck of the balloon to prevent the air escaping.
6. Place the hovercraft on the ground and let go of the balloon

Teacher Tip: Hovercrafts seem to work better if the CD’s shiny side is facing up.

### Extensions

• Drag the hovercraft along the ground with the balloon deflated. Blow up the balloon and do the same thing. Why is it easier to move when the balloon is inflated? Hint: Less friction.
• How can you alter your hovercraft to make it go faster? Slower? (Bigger/smaller balloon). Design an experiment to test your theory.

### Other Resources

Science World Resources | Aéroglisseur maison | French version of this resource

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