Newtonís Third Law Ö.


A friend asked me to help with his daughterís science project.Of course was my answer even before asking what the topic/subject was.Newtonís Third Law was the answer.A dozen ideas came to mind and then I read the rules:no electric components, no CO2 cartridges, no fansÖ no fun at all!


At least they didnít disallow a hand pump so I immediately started thinking about a compressed air pumped rocket Ďengineí.Remembering coke bottle rockets (2L bottles and a foot pump), I tried to assemble a combination of easily available parts to make the power source.


A bicycle pump was a good starting point.Complete with a pressure gauge (alibi not very accurate), Home Depot supplied a pump for $7.00.It has a clip on fitting for the standard tire valve which is nice because it provides a release mechanism (flip the level and wiggle the fitting to launch.


Fitting the 2L bottle with a tire valve turned out to be easier than expected.I bored a 7/16 hole through the cap and then fitted a standard replacement tire valve from the auto parts store.The standard auto tire valve fits into a .453 inch hole which is close enough to 7/16 to fit just fine.Plastic is more forgiving than metal tire rims. Donít forget to unscrew and discard the valve stem otherwise the air canít escape!


The engine when pumped to 20# was able to send a plastic panel with 4 casters across the room.It was tried using water (half full) and a dip tube.The launcher (person) got very wet and the Ďcarí went way up the driveway.



Such a simple rocket engine when under $20 (including pump) and Iím sure you can find many school projects to power.