How Does a Catapult Work?

A catapult is a mechanism used to throw missiles in ancient and medieval warfare. At first, catapults were specifically designed to shoot spears or other missiles at a low trajectory. They were originally distinguished from ballistae and trebuchets, both of which were large military engines used to hurl stones and other missiles, but these distinctions later blurred. Soon after, larger catapults mounted on a single arm also hurled stones, pots of boiling oil, and incendiaries at a high trajectory. They were used to attack or defend fortifications. Catapults were widely employed in siege warfare, but with the introduction of artillery they passed from use. In the 20th century catapults using hydraulic pressure were reintroduced to launch aircraft from warships.

There are several different technologies that fall into the "catapult" category. They include the catapult, the ballista and the trebuchet. The catapult is the winched-down bucket that people normally think about when they hear the word "catapult" (see this page for a picture). A ballista is a very large crossbow (see this page for a picture). A trebuchet is a weighted beam that swings a sling carrying the projectile (see this page for pictures).

Both catapults and ballistas work by storing tension either in twisted ropes or in a flexed piece of wood (in the same way an archery bow does, but on a larger scale).

A trebuchet tends to be easier to build because it consists simply of a pivoting beam and a counterweight that rotates the beam through an arc.

Catapults can launch things a fair distance -- 500 to 1,000 feet (150 to 300 meters) is common. It is surprising how much energy they can store. The gears are important, because they create a winch. The winch allows a person to put a great deal of energy into the catapult over a period of time. Then all of the energy releases at once, throwing the projectile.

Plans for a Spoon-Powered Catapult

Supplies Needed

Strong box

Plastic spoon

Rubber band

Tape and/or scissors

Instructions

  1. Tape the spoon on one end of the box so that the indented part on the part you eat out of is facing toward the box.
  2. Tape one end of the rubber band to the spoon, being certain not to cut the rubber band in half.
  3. Tape or staple the other end of the rubber band to side of the box the indention on the spoon is facing.
  4. Push a stick, nail, etc. into the box right next to the spoon.

Operation

- Put your middle and index finger on either sides of the spoon while placing your thumb on the thin part of the spoon.

- Pull back, load, and release!

Simple Torsion – Powered Catapult

Supplies

A round stick (or a dowel).

A clothes hanger

A cup

Tape

Tool

Pliers

Instructions

  1. Unwind the clothes hanger so it is one long strand.
  2. Wrap the clothes hanger so when one side is pulled back, the other side goes down.
  3. Bend one end back so it overlaps its self. Tape on the cup.

Pull back, load, and release!

Plans for a Torsion-Powered Catapult

Supplies

2or more small screws

3Wooden Base

A small, thin piece of wood (used as moving arm of catapult)

A bent piece of metal to hold the screw down

Stiff, non-copper wire--wire from paper clip works well

Tools

Hammer

Screwdriver

Drill

Pliers

Plans

  1. Wind stiff wire around the large screw, leaving a little unwound wire at both ends.
  2. Hold the screw down to the base and pull one end of the unwound wire toward yourself. The other end should be automatically forced down toward the base if this does not happen, adjust the wire (add of take out/add a ½ turn).
  3. Screw in the piece for holding the large screw down at one end of the large screw. Make sure the large screw is held tightly in place.
  4. Drill a hole the size of the wire into the small piece of wood, length-wise. Push the wire into the hole.
  5. Pull back, load, and fire!

Rubber Band Powered Catapult

Materials

  1. A thin piece of wood and 2 2x4's.
  2. A rubber band or a spring.
  3. String
  4. Nails and/or Screws

Tools

Hammer

Saw

Screwdriver*

*optional

Instructions

  1. Cut one 2x4 so it is about 10" long.
  2. Cut the other 2x4 at about 12" long
  3. Nail/Screw the 2x4's together at the corner so that they form an "L" shape.
  4. Cut the thin piece about 14" long. View Image
  5. Cut a slit in the 10" 2x4. View Image
  6. Put one part of the rubber band toward the top of the thin piece of wood. Loop some string through the rubber band and tie at the other end. Do this to the 10" 2x4. Put the thin piece in the slot made in step 5. View Image

Tie a string to the end of the thin piece of wood. Pull back, load, and fire!

A Twist-to-Fire Catapult

Supplies:

String

Spoon

Wood

Nails/screws

Wire

Tools:

Saw

Hammer and/or screwdriver

Scissors

Wire cutters

Drill*

*optional

Directions:

  1. Saw a 7" x 5" piece of wood. This is the base.
  2. Saw 2 other 1" x 7" pieces of wood.
  3. Nail the pieces of wood together on either side of the base. View Image
  4. Cut two 10" lengths of wire. Wrap one wire around the end part of the wood on the bottom of the base. Wrap the other end around the end of the supporting piece nearest it. Do the same on the other side.
  5. Drill a hole or saw a slit in the top part of each supporting piece. Loop the string through each hole, slit, and tie it. Make sure the string tension is tight. Tape the spoon on. View Image Wind up, load, and fire

Simple Designs