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Q & A: Siege Engines: The Catapult

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Most recent answer: 10/22/2007
When using a catapult to launch a hacky sack, how will the number of rubber bands as the perpulption unit affect the distance the hacky sack will travel? I know when I used more it went farther, why? Also, do you have any ideas that could change my results? Have you attempted a similar experiment? thanks
- Chris Graebe (age 11)
Signal Hill School, Belleville,IL 62223

The idea behing your catapult is that the rubber bands will be stretched and then pull down on the main arm to launch the hacky sack. When you add more rubber bands, it requires more force to pull the arm down. The energy you put into pulling the arm down is held by the rubber bands until you let it go. Then, all the energy in the rubber bands goes into making the sack fly into the air. So in the end, more rubber bands will make the sack fly farther. The easiest way to change our results will be to change the number of rubber bands or the object that you are throwing. Be careful not to break anything. You can also change the arm of the catapult, but that takes a little more work.

I haven’t made a catapult before, but some of my friends made another thing called a trebuchet. A trebuchet is similar to the catapult but insted of using rubber bands, it uses large weights. I couldn’t find any pictures of the one they made, but you can see what a trebuchet looks like at


(published on 10/22/2007)

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