Harford Hills Elementary students build Marshmallow Catapult

By: Bidemi Oladiran (AmeriCorps VISTA)

CAM00208 (1)The Harford Hills elementary after-school STEM program continued on February 23rd, 2016 after a two week hiatus due to snow. The second session encouraged students to design their own marshmallow catapult by using craft sticks and rubber bands to learn about motion and Newton’s first law of motion, also known as the law of inertia. Before they started building the students were asked to explain what they knew about Newton’s first law. What the students learned and what some already knew was that “an object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless an unbalance force acts on it”. An example they were given are seatbelts and why we wear them. If we didn’t wear seatbelts and the car stops, we would keep moving at the same speed the car was moving because there isn’t an unbalanced force to stop us. In the case of the car, the breaks are the force that stops the car, but the seatbelts are the force that stops the passengers from moving after the car has been stopped.

The students were taught how to build their catapults by putting rubber-bands around two sticks, and then stacking eight sticks that were wrapped in rubber-bands. The eight sticks acted as the cross piece or wings which were moved between the two sticks that acted as the base of the catapult. The educators then helped the students hot glue bottle caps towards the top end of the catapult to serve as the launching container. The students were encouraged to decorate their catapults and to test and re-adjust their catapults the same way engineers often have to before deciding on a final prototype.

CAM00207After each student designed their catapults, they competed to see who could launch the marshmallow the farthest. The second test was to see who could accurately get the marshmallow into a container. While none of the students successfully landed in the container, several students came very close. During the tests the students learned that changing the position of the crosspiece provided the greatest distance. In addition to the law of motion, the students also learned about potential and kinetic energy. They learned that potential energy is the stored energy and kinetic energy is what’s being used when in motion. They also learned that if their marshmallows flew too far past the trashcan, then the catapult should not be pushed too far down to reduce the kinetic energy and be able to better aim at the trashcan. But, if the marshmallow barely made it to the trash can, then they needed to increase the kinetic energy by pushing down more on the catapult. At the end of the lesson the students learned about the science behind motion and energy, and they each got to take home their own marshmallow catapult.


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