Physics Project #2 – Catapult
Kristen Zhang & Thanawat Supanitayanon
1999

Plan:

Build a catapult that is less than one meter in height and less than one kilogram in weight. The catapult has to be able to shoot a grade A – large egg over a one-meter tall wall.

Basic structure of the catapult:

Note: the drawing is not drawn to skill.

Step One:

Draw blueprint for the catapult. (See above)

Step Two:

Decide what kind of material to use for building the catapult.

Materials used for the parts of the catapult:

Arm ½ inch PVC pipe

Base and sides ½ inch PVC pipe

Rotation of the arm 2-inch hinge

Seat of the egg badminton ball

Joints / connectors ½ inch PVC joints (Tee and Elbow)

Others screws & rubber bands

Step Three:

Purchase all required materials

Pipes:

Quantity Length Totals

4 1 ft 4 ft

2 0.5 ft 1 ft

2 1.25 ft 2.5 ft

2 0.25 ft 0.5 ft

3 0.5 ft 1.5 ft

1 1.75 ft 1.75 ft

Total length of pipe needed: 11.25

Joints / Connectors:

Type Quantity

Elbow Shaped 6

Tee Shaped 4

Rotation of the Arm:

Type Quantity

2-inch hinge 1

Others:

Type Quantity

Wide Rubber Bands 1 bag (from Wal-Mart)

Screws 1 & those required to attach the hinge

Step Four:

Put all the pieces together.

See diagram below for a detailed look:

Tip: In order to make sure the pipes are securely connected with the joints, use a hammer and gently tap the ends.

This is what we ended up with. With the pieces in the correct places, there shouldn’t be any extra items left.

Step Five:

Apply rubber bands.

For the best result and the most strength, the rubbers are looped. (Doubled) (See diagram.)

Use two strands of rubber bands and loop them with two other rubber bands.

(For a simpler understanding of how we use the rubber bands, the drawing above shows only one band looping the other. However, the actual design has two bands looping two other rubber bands. )

Now that the bands are prepared, loop the ends of the bands onto the pipes. Attach the ends on the top of the stopper (around the arm). Then another (a shorter length) attached on the top of the helper.

Step Six:

Place the seat for the egg.

Many use cups or bottle tops. We had a very different idea! We use the badminton ball (with the top removed) and used it as our seat. It only needs a half-inch screw to attach it securely on the head of the arm of the catapult.