Scientific Principle: Energy
Time: 30 minutes
Catapults have been used throughout history to launch objects at and over the walls of
castles by converting potential energy to kinetic energy . This experiment uses the
same theory, but with projectiles you can eat!
- 2 elastic/rubber bands
- 1 plastic teaspoon
- Masking tape
- 7 wooden skewers
- 5 large marshmallows
- Create a triangle base with three of the wooden skewers, joining them with a marshmallow at each corner.
- Place one skewer upright into the centre of each of the three marshmallows used in the base then bring the tips of the skewers together to transform your triangle into a pyramid.
- Secure the three skewer tips with an elastic band, then place a marshmallow over the top.
- Use masking tape to attach the spoon to the end of the final skewer.
- Feed the spoon-skewer combo through the centre of the pyramid, placing the wooden end into the base triangle marshmallow at the front of the structure and holding the spoon end at the back of the structure.
- Place the second rubber band over the top of the pyramid and loop it under the spoon to hold the spoon off the ground.
- Place a marshmallow on the end of the spoon, pull it backwards against the rubber
band and let go!
The Science Behind Marshmallow Catapults
Catapults work by converting energy from one type to another and transferring this energy from one object to another. When the spoon is pulled back against the rubber band, energy is added to the catapult system. This energy is stored as potential energy in both the spoon and the rubber band. The further the spoon is pulled back, the more potential energy is stored. When the spoon is released, the potential energy converts to kinetic energy ( energy in motion) and the spoon propels forward, releasing the energy stored in it. This energy is transferred from the spoon to the projectile marshmallow sitting in the spoon and causes the marshmallow to fly through the air. Because the spoon and skewer combo are long and bendy, they act as a lever, pivoting on the marshmallow base and enabling the projectile to be propelled a long way relative to the small amount of effort.
- What happens if you shorten the length of the spoon-skewer combo? Why do you think that is?
- Can you construct a catapult using a shape other than a pyramid? How about a square or a rectangle?
- How does changing the length of the rubber band affect how the marshmallow flies?
- Can you aim the marshmallow so that it lands in a bowl across the table?