A catapult uses tension to fling a projectile across a far distance. The stored energy is released and 'transfers' into velocity which pushes the projectile onwards. In the case of a mousetrap catapult, the tension comes from the springs in the mousetrap. To build a catapult, you will need a mousetrap, electrical tape, pliers, a jumbo popsicle stick, some kind of holder for the projectile, and
erasers.
Building a Mousetrap Catapult:
1) Remove the catch and the hold-down bar using the pliers
2) Tape erasers in front of the springs so that they lean back slightly (you want to achieve a 45º angle)
3) Attach jumbo popsicle stick to the hammer using electrical tape and attack the 'holder' for your projectile
4) Release!
The Physics Behind a Catapult
Catapults use the elastic potential energy that is stored within the spring/launch mechanism of the catapult to launch the payload or projectile. The potential energy is transferred into mechanical energy when the projectile is launched. When you stretch the catapult's elastic you are increasing the potential energy thus creating an accelerating projectile.
Keep in mind:
- 45º gives maximum horizontal displacement
- A longer catapult arm does not necessarily translate into a further horizontal displacement
Types of Catapults
Trebuchet - heavy payload & long distance
-uses energy of a falling counterweight to launch projectile with a high speed
-a counterweight that is much heavier than the payload produces maximum launch speed because
that means that it will fall quickly
Mangonel - launch velocity equals velocity of the arm near the projectile holder/bucket
-uses a crossbar to stop the arm at the desired angle
-launches projectiles best at lower angles with a large range
-not as energy efficient as a trebuchet because the stored energy goes towards accelerating the arm,
which means wasted energy
Onager - nearly identical to the trebuchet except that it uses a torsion bundle to rotate the arm
-allows for a greater throwing distance than the mangonel but this distance was not consistent due to
the wearing down of the tension source
Ballista - 'large crossbow'
-uses twisted ropes as the energy source
-used to launch darts, bolts, and spears great accuracy and force
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| Trebuchet |
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Ballista |
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| Mangonel |
