What you need

• Two large plastic bottles
• A washer
• Water
• Duct tape
• Food colouring

Instructions

1. Fill one bottle two-thirds full with coloured water Turn the other upside down, put a washer between them and tape the joint firmly
2. Turn them upside down, let the water flow normally, then swirl the bottles around vigorously

Results and Explanation

When you swirl the water, it forms a vortex like a tornado and flows much faster into the lower bottle.

Air from the lower bottle rushes to the top through a hole in the middle of the vortex as the fast-flowing water drains rapidly at the edges.

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.