Charlie

A simple rocket can be built of an empty Coke or lemonade plastic bottle. Partly filled with water and pressurized air the rocket can be blasted high up in the air. The pressurized air expels the water, which in turn creates the thrust to accelerate the rocket, counteracted by the air resistance and the weight of the rocket. Maxmum speeds are up to 200 km/h and the world record height is more than 300 m!

How Water Rockets work

The bottle is partially filled with water and sealed. The bottle is then pressurized with a gas, usually compressed air from a air compressor, or cylinder, but sometimes CO₂ or nitrogen from a cylinder.

Water and gas are used in combination, with the gas providing a means to store potential energy, as it is easily compressed, and the water increasing the mass fraction and providing greater momentum when ejected from the rocket's nozzle.

The seal on the nozzle of the rocket is then released and rapid expulsion of water occurs, at high exhaust speeds. Until the propellant has been completely expelled, and the pressure equalizes with atmospheric pressure, there is a net force created on the tank in accordance with Newton's third law. The expulsion of the water thus can cause the rocket to leap a considerable distance into the air.

In addition to aerodynamic considerations, altitude and flight duration are dependent upon the volume of water, the initial pressure, the rocket nozzle's size, and the unloaded weight of the rocket. The relationship between these factors is complex and several simulators have been written by enthusiasts to explore these and other factors .

Flying model rockets is a relatively safe and inexpensive way for students to learn the basics of forces and the response of a vehicle to external forces. A model rocket is subjected to four forces in flight; weight, thrust, and the aerodynamic forces, lift and drag. There are many different types of model rockets. One of the first and simplest

On the figure we show a generic launcher, although launchers come in a wide variety of shapes and sizes. The launcher has a base to support the rocket during launch. A hollow launch tube is mounted perpendicular to the base and is inserted into the base of the rocket before launch. The launch tube is connected to an air pump by a hollow feeder line.

The other part of the water rocket system is the rocket itself. Usually the rocket is made from a 2-liter soda pop bottle. Before launch, the bottle is filled with some amount of water, which acts as the "propellant" for the launch. Since water is about 100 times heavier than air, the expelled water produces more thrust than compressed air alone. The base of the bottle is only slightly larger than the launch tube. When the rocket is placed on the launch tube, the body tube becomes a closed pressure vessel. The pressure inside the body tube equals the pressure produced by the air pump. Fins are attached to the bottom of the body tube to provide stability during the flight.