|A polystyrene cup, full of water|
A carpet - office type carpets definitely work well. Make sure it doesn't matter if it gets wet...
Push the cup across the carpet, slowly, do you notice anything about the cup?
Speed up your pushing until you see some strange effects
|As you start the water will start to vibrate||It will form waves of different shapes and patterns|
|It will get more and more disturbed as you speed up.||Until it forms spouts fountaining out of the cup.|
Here is a video of the effect.
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.
|This will create a sreies of circularish waves from the edges.||The sloshing will tend to distort the cup producing more waves from the sides of 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.