Water Rocket

To explain how rockets work we use water rockets. Basically, it's a half litre drinks bottle half-filled with water, with a special valve on the end. Air is pumped into the bottle until the air pressure gets high enough to blow the valve out. What follows is a practical demonstration of Newton's Third Law in action. Great fun! Here, the rocket has just taken off and exited the picture. I like the fact that you can trace the path of the rocket by looking at its trail of water.