How to Make a Simple Catapult Launch a Tennis Ball

Measure a 2-by-4-foot rectangle on the plywood sheet. Outline the measurements with a pencil. Use saw to cut out the rectangle, which will serve as the catapult platform.

Draw two rectangles where the catapult legs will stand. These should be spaced 1 foot from each other in the center of the platform. Lift up the platform so it is vertical. Place one 2-by-4-inch piece of 3-foot wood on the platform. Drill two wood screws from the bottom of the platform up into the 3-foot leg. Do this again for the second 3-foot leg.

Measure two identical triangles on the leftover plywood. These triangles should be at least 2-by-3 feet. Screw these on the outside of each catapult leg with one screw at the bottom of the triangle and one at the top. The triangles should face outward and sit flush against the platform. Lift the platform again and drill two screws into each triangle base to secure it to the platform.

Bore out two identical holes, 1 inch in diameter, 2 inches from the top of each catapult leg, with the drill. Take the 2-by-4 piece of wood that is 4 foot long and bore a 1-inch hole in the center. This will serve as the catapult arm.

Apply wood glue on both ends of the wooden dowel. Insert through both catapult leg holes and the center of the catapult arm, with the catapult arm being in the center. Let the glue dry for at least an hour.

Drill pilot holes on the center of each catapult arm, 1 inch below the wooden dowel. Drive screw-in hooks into each arm. Attach bungee chord to both hooks, making sure that is taut. When the catapult arm is pulled back against the bungee chord, the tension will increase. As soon as the catapult arm is released, the bungee chord will snap back into position, sending the tennis ball flying into the air.

Screw plastic cup to the end of the catapult arm. Load it up with a tennis ball and prepare to fire.