Drink Bottle Rocket

that really flies.

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Purpose -

A great way to show Newton's third law of motion.  Also demonstrates the compressibility of gases compared to liquids.  

Nature - 

Demonstration

Materials - 

A commercially purchased Bottle Rockit© Kit 

or 

a rubber stopper that jams tight in the neck of a plastic (PET) 2 litre soft drink bottle, electric drill and bits, a bicycle pump, a pump attachment for inflating balls, a tripod

Method - 

· If using a the Bottle Rockit© Kit simply follow the instructions on the box (Photo 1).

· To make your own first drill a hole through the rubber stopper that will just allow the ball attachment to squeeze through (see Photo 2)

· One quarter fill a 2 litre soft drink bottle with water and jam the stopper into the mouth.

· Turn the Bottle upside down and set in tripod for launch.  Screw bicycle pump onto attachment and start pumping  After a fair number of pumps the bottle will launch into the air.

Safety -

Care needs to be taken that the rocket does not hit anyone either during launch or as it falls back to earth. 

Explanation -

As more and more air is compressed into the bottle, the pressure inside grows.  This begins to push the stopper out of the neck of the bottle, until it finally releases.  Because there is water in the way, the air pushes it out of the bottle as it tries to escape.  This forces the bottle to fly through the air as a rocket. 

Notes -

This nicely demonstrates Newton's third law of motion :-

For every action there is an equal and opposite reaction. 

The rocket (or more precisely the air in the rocket) pushes against the water, so the water pushes back against the rocket causing it to move.