# Catapult Physics!

Physics:

Simple Machines– this is a great chance to discuss simple machines but in particular, the lever. Catapults and trebuchets use a lever to do work. Students can research the different classes of levers and see how changing the placement of the fulcrum changes the performance of their machine.
Similar to the mechanics of the machines, how does the machine do the work? They all transfer large amounts of potential energy into kinetic energy. Some do it more efficiently than others.

• Which one works best?
• How can you test it?
• Make the hypothesis and make plans to build the machine so you can test it!

For older students, there are all sorts of calculations you can do on the energy efficiency of the machines. In a quick search, I found a website dedicated to Experiments with Trebuchets. The author, Mr. Bullock, gives plenty of instructions and advice on building the trebuchets and has an entire section on the math. All the variables are listed in working out the formula for the Energy Efficiency which is the Kinetic Energy/Potential Energy. Of course you’d need to derive the numbers for Kinetic and Potential Energy which would be great fun using the list of variables provided. I may not be right on target with my answers, but admittedly I have a curiosity about physics and math so this is something I’d encourage my older children to try!
Again, this unit study isn’t about exhausting all the planning tools you have. It’s about getting your students excited about an exploration and not worrying if everything is in place first. It’s about a quick web search and doing and having fun.

Tomorrow, we’ll have a contest to see which catapult performs the best!
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