You and your children can enjoy and learn science together by building a water rocket. All you need are a plastic soda pop bottle partially filled with water and a bicycle pump to launch it. You can also construct a launching pad from materials commonly found in a hardware store.
A water rocket works based on Newton’s Third Law of Motion: “For every action, there is an opposite and equal reaction.” The action is the expulsion of water by the pressurized air from a nozzle connected to the pump or launching pad. The reaction is the forward motion of the rocket as the walls of the soda bottle are pushed by the pressure.
The major part of the water rocket is the body made from a soda pop bottle. A beginner can start with a 250-ml lemonade bottle then later use a 2-liter cola bottle. A nozzle or connector is attached to the bottle opening to help propel the rocket. It also provides a mounting point for launchers.
You can add a nose cone cut from plastic bottles to improve the aerodynamics of the rocket. It can come in different shapes and sizes. Fins taped to the sides of the bottle will stabilize it.
Air resistance and the weight of the rocket determine the speed and height that is reached. Experiments by high school students in the US have shown that an initial pressure of about 6 bars propels the rocket to 50 meters. Water rockets have been recorded to go as high as 500 meters, with speeds over 100 miles per hour.