2 x 2l bottles
Duct tape or electrical tape
Oil and Dye (optional)
What to do:
1. Fill one of the bottles two thirds full of water
2. Put the empty one on top of the bottle with water in it and tape the necks together securely
3. Turn the bottles upside down and watch what happens.
4. Repeat again but this time swirl the water
How does it work?
It’s all about the spin. It is the same principle that helps a hurricane force winds to speed up.
The reason why the 1st attempt took longer than the second is because the space in the upper bottle needs to be filled with air to replace the space that was taken up by the water else it would leave behind a vacuum. The air from the bottom bottle rises through the narrow neck to do this. However, while the water is flowing downwards and the air is pushing upwards the air bubbles slows the water flow down.
In the 2nd attempt however, where the bottles are swirled, as the water is goes through the necks of the bottles it is forced to go in to tighter and tighter circles – the same principle applies to pirouetting ice skaters; they rotate quicker when their arms are pulled into their bodies – these tight circles make a gap in the centre of the necks and allow air to flow freely through which allows the water to flow freely into the bottle below as there are no obstructions.