60 Second STEM: Catapults

Supplies:

8 Popsicle or craft sticks
4 Rubber bands

Directions:

Stack 6 of the craft sticks and bind them on each end with a rubber band. You should end up with tightly bound stack.
Stack 2 craft sticks and bind them tightly on one end with a rubber band.
Open the stack of 2 craft sticks such that the flat ends are facing one another and slide the stack of 6 craft sticks between them so that the flat side of the stack of 6 rests against the flat side of the stack of 2.
Secure the craft sticks by wrapping a rubber band around the point where the stack of 6 and stack of two meet as in the picture below.

Make it an experiment:

Try moving the stack of 6 craft sticks around and testing how far you are able to launch objects (such as a small ball of paper). Does moving the stack of 6 craft sticks closer to the bound end mean that your balls launch further? What about moving in the other direction?

What’s happening:

With this investigation, we are exploring a lever which is a type of simple machine. A lever has three essential components: load, effort and the fulcrum or pivot point. The load and effort refer to the input and output force and the fulcrum is the point that the lever rotates around. In this case our catapult is a class 1 lever meaning that the fulcrum sits between the effort and load. Our fulcrum here is the stack of 6 craft sticks as this is what the arm of the lever is rotating around. The load and effort are the bound end and the end which you push down on to launch an object. As you move the fulcrum around, you change the length of the lever arm which changes not only the speed with which it can bounce back up but also the amount of effort available to launch your object. Interestingly, you can see this effect even before you launch if you look at the rubberband on the bound end of the lever. When the fulcrum is close to the bound end, pushing down on the loose craft sticks makes the rubber band on the bound end stretch which does not happen if the fulcrum is far away from this end.

The Video:

Click here to watch Hannah from Shoestring Science explain and complete this investigation