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Building a Catapult for physics

Updated on May 29, 2016

Building a catapult for a physics project can be a hard job for those who do not know how to do it. I recently had to build one for class and I had no Idea how to start. I searched online for help with building it, I asked people I know for help, and all it seemed to do was make the task harder for me. So in this guide I am going to show you the basics of how to make a Catapult work.

Starting the project

First off you need to know what the guidelines for your project are. If you do not know ask your teacher. My project called for the catapult not to be bigger than four feet in length, four feet wide, and four feet in height. My catapult had to shoot a tennis ball either 30 feet, 35 feet, or 40 feet. My teacher picked a random distance by putting those three distance in a hat and picking one. So I started simple I found a picture of a catapult online and started to built it. Now this is not a how to guide, this is me explaining what I did to get this project to work. I built the basic shape of the catapult and then came the hard part making the catapult work.

Making the catapult work

First off I used bungee cords that I bought at Walmart. That was disappointing, the tennis ball barely made it ten feet. So next off my dad and I went to Lowe's and bought a spring. I put the spring on and the tennis ball shot 20 feet. I knew that I was on to something so, I decided to move the crossbar on the catapult a little. Moving the cross bar at different angles can make the projectile go farther. You will want the arm of the catapult to hit the crossbar at an angle. Hitting at an angle means more of an arc, which turns into the projectile going further. So I did this and the tennis ball went 55 feet with the crossbar at an angle.

So I decide that maybe I could somehow change the way the catapult shoots.I put a piece of wood in the back of the catapult, I then screwed hooks into the wood at different levels. These hooks in the wood made would make the arm of the catapult go lower or higher. I did this because placing the hook at the bottom where the hooks usually are made the catapult shoot too far. The hooks and the spring can be seen in the picture above. After testing the arm at the different hooks, I was able to get the distances that I need and my catapult worked.


Do not be afraid the spring will stretch on the catapult. As you can see in the picture above I drilled a hole into the crossbar for the catapult to stop the spring from stretching.

The metal rod at the bottom of the catapult that made the catapult shoot was flimsy but still worked. I suggest that you use a thick metal rod. So that the pressure does not make the rod bend.

Also have an adult close by to help put on the spring. I bought a really strong spring, it cost me about $6. After you get used to taking the spring on and off it gets easier.

The earlier the release of the projectile means more of an arc to. If you can not move around the crossbar find something to make the release earlier. You can place an extra piece of wood on the crossbar.

More tips

Do your own research. There are plenty of helpful things out there for you to use and get inspiration from.

Mark out your yard or wherever you will be shooting to make knowing how far you shot easier.

Most of all do not wait until the last minute to do this. This is not a project that you can throw together at the last minute and except to get a good grade on.

This is a great video that I found while building my project.

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