Lesson 21: Clothespin Catapult

Ancient people teach us a thing or two about energy when they laid siege to an enemy town. Although we won’t do this today, we will explore some of the important physics concepts about energy that they have to teach us by making a simple catapult.


  • Clothespin
  • Popsicle Stick
  • Spoon
  • Hot glue gun
  • Scrap of wood or cardboard
  • Ping pong ball or something lightweight to toss

Download the student worksheet that goes with this lesson.

All the different forms of energy (heat, electrical, nuclear, sound etc.) can be broken down into two categories, potential and kinetic energy.

Think of potential energy the “could” energy. The battery “could” power the flashlight. The light “could” turn on. I “could” make a sound. Kinetic energy is the energy of motion. Kinetic energy is an expression of the fact that a moving object can do work on anything it hits. We’re utilizing the “springy-ness” in the popsicle stick, spoon, and the torsion spring to fling the ball around the room. By moving the fulcrum as far from the ball launch pad as possible (on the catapult), you get a greater distance to press down and release the projectile.