Work, Energy and the Power of Rubberbands

What are work and energy and how are these important concepts related to each other? This is what I ask my eigth grade students at the start of our unit on conservation of energy.

Work is a hard term to define in physics. While sitting quietly and “working” at their desks, students often comment that they have too much “work” to do or that something is a lot of “work”. But unless you are just sitting there pushing your iPad back and forth across the tabletop, chances are you are doing little if no real work. That is because in order to do work in physics a force must be applied to an object to move it through a distance. It doesn’t matter how hard you push on something — if the object does not move, then no work is done.

A great way for students to explore the relationship between work and energy is to have them build cars that are powered only by rubberbands. Stretching a rubberband stores energy in it that can later be used to power the car. Besides the basic physics concepts, students must also consider the design and technology elements of their cars. To receive full credit in my class, their car should travel in a straight line for at least 10 meters.

After students build their cars it’s race time. Who can cover 10 meters in the shortest amount of time? To get things started, the rubberbands are wound around the rear axel of each car. In doing so a force is applied over a distance and potential energy is stored in the rubberband. This gives the rubberband the potential to do work. Hold it tight, place it on the floor and away it goes, gaining velocity as potential energy is converted into kinetic energy.  

Popsicle stick catapults and spinning cup helicopters are other great activities that help students learn about how energy can be stored in elastic materials and then put to work. Work and energy, you can’t have one without the other.

To learn more about this topic, check out my full energy, work and power playlist.

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