Great clip from last nights “Bang Goes the Theory” – a water powered jetpack

and remember, don’t try this at home.

A simple rocket made from a coke bottle, 1/4 filled with water and powered by a bicycle pump. (Can buy the kit from Hawkins Bazaar for about £12.99 here)

Great for talking about Forces. Make sure you do it somewhere where there’s a lot of space

Update – from www.Rokit.com

Science Education: Using ROKIT to “Bring Science Alive”

• A precision water rocket that self launches at a pre-determined pressure (2BAR).
• Providing the capability of repeatable experiments.
• Schools, colleges and Science Advisors throughout the world are using this exciting kit to demonstrate Laws of Motion.
• Rokit is a valuable visual tool for all levels of Science Education.

ROKIT for Primary Education demonstrates the principles of rocket propulsion, trajectory, streamlining and basic aerodynamics. It is also used in fun education projects such as ROKIT Golf, Space Travel etc.

ROKIT for Secondary Education is a precision water rocket that enables accurate and repeatable experiments to be performed. It can be used to measure and study velocity and acceleration, force, trajectory, thrust and drag.

About Rockets

A squid propels itself by filling its body with water and ejecting it backwards in order to move forwards. This is the principle used by rocket engineers. Space rockets use fuels that are burned in a chamber shaped rather like a bottle, with the neck pointing backwards. The burning fuel produces a large quantity of gas that is further expanded by the heat generated and this is ejected through the neck (or nozzle) of the “bottle” (normally called the combustion chamber) at a very high velocity, propelling the rocket in the opposite direction.

The ROKIT, like the squid, uses water as the driving agent and compressed air instead of heat to provide the energy.

For the technically minded the pressure in the bottle at launch (just before the brass bung releases) is about 18 x 104 N/m2 (or about 25 psi). The water is forced through a nozzle with a cross sectional area of about 1cm2 and this produces a theoretical thrust of about 18 Newtons (about 3.9lbs) at launch. As the water is ejected the ROKIT gets lighter resulting in an increased acceleration or ‘g’ force. This increasing ‘g’ force is one of the more unpleasant aspects of space flight that astronauts have to endure; a rocket leaving the earth’s atmosphere would have to keep up this increasing acceleration for some time. The ROKIT expels its charge of water in about 1 second so DON’T WORRY, IT’S NOT LIKELY TO GO INTO ORBIT!

What happens when you drop a heavy object and a light object at the same time? Well they should hit the ground at exactly the same time. This is because the pull of gravity is the same on each one, and so they accelerate at the same rate.

On Earth it’s hard to visualise this since air resistance also gets involved – and so if you drop a hammer and a feather the feather floats down slower than the hammer.

On the moon, there is no air, so air resistance does not affect the result. One of the experiments carried out by the Apollo astronauts on the moon was to demonstrate a hammer and feather drop and as you can see, without air resistance both the hammer and feather hit the ground at the same time.