They are designed to send golf balls flying at insane speeds reaching up to or over 40 yards in distance.
Depending on your own construction, the catapult explained here was recorded to have an acceleration of 235 m/s/s, and could probably more if built more effectively then ours!
Construction is simple and requires only basic tools that are likely already somewhere around your house.
This took several days, but could be accomplished in a few hours, most likely, if you were dedicated enough and had all supplies ahead of time.
We did this mainly because of our study of motion and its related laws, including the law of gravity and Newton's Second Law.
Step 1: Materials
Five 2-foot planks of wood(pref. 2x4)
Two 3-foot planks of wood(pref. 2x4)
Some form of pivot arm(can be vaired in width; must be over 2 feet long.
Wood or metal arm which can be used to throw golf-ball
Power-drill and drill bits
Two trampoline springs
Two 'circle' screws (i.e. pieces of metal which can be screwed into wood, the opposite end of which has a circular head which the springs can latch onto.) (See picture below if you don't understand.)