DIY CD Hovercraft
Sun, 9th May 2010
Download as mp3
from the show Does Beer Kill Brain Cells?
What you Need
A round party balloon
An old CD
A piece of card
A biro lid
What to do
First make a cone from the card so that the top end is about the same size as the pen lid and the bottom is bigger than the hole in the CD
Put the CD with the shiny side upwards and then tape the cone over the hole. Try to seal it as well as you can.
Put the pen lid in the top of the cone and tape it in without blocking the hole.
Put the balloon over the CD. Blow the CD up through the hole in the CD and then put the hovercraft onto a flat surface.
What may happen
You should find that the CD floats slightly above the table with very little friction.
Why does it happen?
The air is blown out of the balloon under the CD. If the CD is close to the table, the air pressure under the CD is higher than above it. This applies an upward pressure on the CD making it float on air, hugely reducing the friction between the cd and the table.
The air is pushed under the CD by the balloon...
The air under the CD will be at a higher pressure than the air around it so the CD is pushed upwards
If the surface isn't smooth enough the air can escape through the lower areas without the CD lifting off the higher areas, which is why it doesn't work on a carpet.
If the hovercraft is on a rough surface the air can escape through the low areas without building up enough pressure for it to float
You can actually get the same effect by just blowing down the hole of the CD.