Physics Week Nine

For our Physics class this past week, we learned a little about Newton's Third Law of Motion, and we played with matches.  :-)


Newton's Third Law of Motion - for every action there is an equal and opposite reaction.

This Law can be seen in action when you release the air from a balloon - air escapes in one direction and the balloon flies in the other direction.

A match rocket illustrates the principle of rocket propulsion in a simple, small-scale "rocket."  The burning match head forces out hot, expanding gases from the jet exhaust ports at high velocity, propelling the rocket forward... when all goes well!  The rocket has one or two ports, or openings, to vent the gas in a controlled direction.  If the gas is exerting a force in the backward direction, the equal and opposite reaction will cause the rocket to move forward.

There are a couple of different ways to make match rockets, and they can be made with either wood or paper matches. William Gurstelle's book, Backyard Ballistics, offers instructions for making paper match rockets, along with a fairly elaborate launch platform.

The website Physics Central offers instructions for a wooden match rocket, with a very simple launch platform made from a paper clip.  Landon and I tried both paper and wood matches at home, and both worked, but when using a paper clip launch platform, we found that the wood match, being longer, worked better.

At co-op we briefly discussed Newton's Third Law and how the match rockets worked, then went outside to try our hand at making them.  Match rockets aren't difficult to make, but it requires some patience to make them well.  And we found that weather conditions for the launch matter too - there was just enough of a breeze that we had some trouble getting any very successful flights.  Probably the best we managed was a few feet.  But we had fun anyway, and didn't burn anything that we shouldn't have.

This is the ninth post in a series -

• Physics Week One (gravity and friction)
• Physics Week Two (structural engineering)
• Physics Week Three (suspension bridges)
• Physics Week Four (constructing catapults)
• Physics Week Five (catapults)
• Physics Week Six (constructing trebuchets)
• Physics Week Seven (trebuchets)
• Physics Week Eight (Viking catapult and hand slings)

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