During our physics class, while we were learning acceleration,speed,force, and etc.. We decided to build a catapult since the arm puts acceleration,speed, and force into the invention. So our class decided to test how far we can launch the golf balls by building a mini- catapult (because of the small doors) also we could design it anyway we wanted. But first we needed to know what we were going to bring, so for ours we had at least 4 large 2X4's, a can for the "hand", a metal pipe for the arm, 2 large springs, and a steel pipe for latching the springs with the pipe. Also we tested our catapults acceleration and it came up to 125 m/s squared. Which the according to Newton's Second Law the golf ball's distance should've went about 76 but our final was 22.8m which was less then we expected out of our catapult. So this is how we built it:
L