Teaching ScienceHelp for trainee Science teachers

The Diet coke and Mentos guys from Eepybird are back with their new venture – a rocket car!

From the BBC’s Bang Goes the Theory site.

Full instructions can be found here.

Rockets work by ejecting something out of the back and a so-called ‘reaction force’ then pushes the body of the rocket forward.

Here, water and air are shoved out the back. The water is heavier so that’s what gives the bottle the main kick forwards.

The energy to force the water out is stored as air pressure inside the bottle. You supply the energy as you pump air into the bottle.

The air pressure inside builds up and pushes on the water. But friction holds the cork in place and that pushes back on the water, so for a while nothing moves.

Once the friction force can no longer contain the pressure, the cork is shoved out and the pressure then acts on the water to eject it from the bottle.

Compared to the bottle, the water is heavy. So pushing water out at a moderate speed backwards gives the bottle a lot of forward speed.

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!