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How to Make a Catapult to Launch a Ping-Pong Ball

A ping-pong ball is never going to smash down a fortress wall, but it does make a nice projectile for a catapult. It's light, reasonably aerodynamic, bounces and doesn't break too easily if you avoid stepping on it. What's more, a catapult on this scale can be built with everyday materials and can be used for science projects or math investigations in the classroom. Catapult building is all about fine-tuning, so why not have a competition in which everyone gets the same materials but is free to modify the design as they please?

Things You'll Need

5 wooden rulers 12" long
Drill
5 carriage bolts
20 nuts fitting the carriage bolts
Brick with three air gap holes
Small plastic cup
Sticky tape
Small dumbbell weight
String

Instructions

- 1
  Drill holes in the rulers large enough for the carriage bolts to fit through. Use the measurements given on the ruler as a guide for where to drill the holes. Make the holes as centrally as possible. Drill holes in four of the rulers 1/2 an inch from the end and, measuring from the same end, 10 inches from the end. In the last ruler, drill at 1/2 an inch and 3 1/2 inches from the end.
- 2
  Lay the brick with one of its long, narrow edges on the table. Take one of the four rulers with the shared sets of holes. The brick has a set of three holes in a row which act as an air gap. Start with one of the holes on either side, but not the middle one. Take the ruler and position the hole that you drilled 1/2 an inch from its end and place it over the air gap hole. Push a carriage bolt through the hole in the ruler, through the air gap hole and out the other side of the brick. Slide the 1/2-inch hole of another ruler over the protruding end of the carriage bolt. Tighten a nut over the end.
- 3
  Do the same with the second pair of rulers using the air gap hole at the other end of the brick. Bring the ends of the rulers on each side of the brick together to make triangles. Overlap the 10-inch holes of the rulers on each side of the brick. Slide a carriage bolt in through the first pair, then attach a nut and screw it tight against the rulers.
- 4
  Add another nut and position in the center of the carriage bolt. Take the remaining ruler and slide it on to the bolt, slipping the bolt through its central hole. Fix another nut on the other side of it. Slide the tip of the bolt through the hole in the remaining pair of rulers with a nut on each side of them to keep it tightly in place.
- 5
  Drill another set of holes just where the rulers which form the triangles come up over the edge of the brick. Slide carriage bolts through these holes and fasten in place with nuts.
- 6
  Tie the dumbbell weight to the short end of the central ruler, putting the string through the 1/2-inch hole. Place the plastic cup against the other end of the ruler and tape into place. Pull down the cup end of the catapult, place the ping-pong ball inside and fire.

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