Cup Fountain

Make a fountain, and some fascinating patterns with a polystyrene cup and a piece of carpet.

What you need

What to Do

Push the cup across the carpet, slowly, do you notice anything about the cup?

Speed up your pushing until you see some strange effects

What may Happen

Here is a video of the effect.

What is going on?

As you push the cup along the carpet it will tend to stick and slip, and stick and slip. 

 This will start to vibrate the water creating waves leaving the front and back fo the cup.

 These waves then get reflected and interact with one another forming a very disturbed surface.

If in a region of this surface you get a circle of wave converging on a point, this wave is going to get higher and higher as all the energy from the circle of waves is concentrated.

In fact as the waves crash into one another at the centre their kinetic energy will tend to get directed upwards into a great big spike.

If this spike is long enough the end can break away as a droplet and fly off and out of the cup.

Written by Dave Ansell