Rise and Fall by Invisible Force

Have you ever played volleyball, a game where you try to hit a ball back and forth over a net without letting it touch the ground? Can you imagine building a machine—actually, two machines, one on each side of the net—to do that instead? That is what we will do in this engineering design project, but we will not use a full-sized volleyball. Instead, we will try to launch a ping pong ball back and forth over a much smaller “net” (a folded piece of paper).

This project allows us to explore some interesting topics in physics and engineering. It’s a great opportunity to learn about simple machines such as the lever or the inclined plane. Here we can also investigate more complex machines like catapults and slingshots, which are used to launch projectiles. Just think about how you could incorporate different aspects of these machines into your design.

The ball needs kinetic energy, the energy of motion, in order to fly through the air. Where will that energy come from? It could come from elastic potential energy, the energy stored in stretched material, like a rubber band. it could come from gravitational potential energy. The energy stored in an object that is raised off the ground could come from work that you do with your hand by exerting a force.

Finally, we can use this project to demonstrate the engineering design process. It is unlikely that you will think of an idea for a machine, sit down and build it, and have it work perfectly on the first try. Just encourage students to come up their own designs, test the designs and modify the designs to improve them.

Professional engineers rarely get things right on the first try!

1. Building a machine that can launch and return a ping pong ball back and forth over a net.
2. Understanding the relation between forces, motion and energy and projectile motion.
3. Understanding that kinetic energy depends on mass of an object.

1. How could you build a machine to launch a ball by using these materials?
2. Where will the energy to launch the ball come from?
3. Which device could you build to catch the ball without dropping it?
4. How can you get the ball back over the net?
5. How could your machine convert one form of energy into another?
6. Which trajectory (path the ball takes through the air) will make it easier to catch the ball or get it over the net: a high, steep trajectory or a low, shallow trajectory?