Cup Trick

What you need

• Two identical paper or plastic cups

Instructions

1. Take two empty cups and put one inside the other
2. Hold them quite close to your mouth and blow between the rims of the cups

Results and Explanation

If you blow softly the inner cup rises up slowly. If you blow hard the top cup launches itself across the room.



Moving air has a lower pressure than still air, so, as you blow, you lower the air pressure between the rims. As the still air in the bottom of the cup is at a higher pressure, it forces the top cup up and out.

These experiments have not been specifically safety tested for home use but we believe them to be safe if the instructions are followed. Adult supervision or direction is recommended as appropriate. All experiments are carried out at your own risk.