DIY CD Hovercraft

09 May 2010

Ingredients

Balloon A round party balloon A CD An old CD
Card A piece of card Tape Some tape
Biro Lid A biro lid

Instructions

Card Cone 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
CD with cone 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.
Pen top in cone Put the pen lid in the top of the cone and tape it in without blocking the hole.
The cd hovercraft 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.

Result

You should find that the CD floats slightly above the table with very little friction.

&nb

CD hovercraft

Explanation

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.

Airflow around the CD
The air is pushed under the CD by the balloon...
Pressure under hovercraft
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.

Hovercraft 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.

Making a CD hover by blowing

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