The Energy Can



The Energy Can demonstrates stored and kinetic energy. If you are interested in your student doing this project, you will need:

an empty coffee can (1-lb. and 5'' diameter w/plastic lid)
Fishing sinker (1 oz.)
Hammer
1-2 Long Rubber-bands (6'')
2 paper-clips
nail
With a hammer and nail, punch one hole through the bottom of the can and one in the center of the plastic lid. 

Thread the paper-clip onto one end of the rubber-band. Then thread the other end of the rubber-band through the hole in the bottom of your can. The clip should be on the outside of the can.
Slide the sinker onto the middle of the rubber-band.
Thread the free end of the rubber-band through the hole in the lid.
Attach the paper-clip to the rubber-band on the plastic lid so the band won't slip into the can.
Place the plastic lid tightly onto the end of the can.
Now you can explore potential and kinetic energy with this toy. Keep in mind the mathematical formula:

Potential Energy + Kinetic Energy = Total Energy

Can you predict where the potential energy is going to be the highest? Where is the kinetic energy going to be the highest?

Once you have made your predictions, push the Energy Can slowly across a smooth floor, and watch it travel until it stops by itself. Now, push it rapidly across the floor and watch it until it stops.
What did the Energy Can do when pushed slowly?
What did the Energy Can do when pushed rapidly?
How is the behavior of the Energy Can different from an ordinary can?

What conclusions can you make? 
Why do you think the Energy Can acts differently from an ordinary can? 
Where was potential energy the highest? Why?
Where was the kinetic energy the highest? Why?
Where is the potential energy the highest on a roller coaster?
Where is the kinetic energy the highest on a roller coaster?

As the Energy Can travels, some of its kinetic energy is changed to thermal (heat) energy in the form of friction. The thermal energy is waster kinetic energy. It does not help the Energy Can move so the can slows down. The potential energy was highest at the point where the Energy Can stopped moving away from you after the first push because that is where the most energy was stored inside it. Later trips lose more and more kinetic energy to friction, so it cannot build up as much potential energy. 
The same thing happens with a roller coaster. As the coaster train is towed by electrical energy to the top of the first hill, the train gathers potential energy. The top of the first hill is where the train has the most potential energy. As the train travels to the bottom of the first hill, this potential energy is converted to kinetic energy. The bottom of the first hill is where the kinetic energy is the highest. The total potential and kinetic energy can never be more that what the electrical energy gave the train. In addition, friction converts some of the kinetic energy into thermal energy instead of movement, wasting some of the kinetic energy. 

The Law of Conservation of Energy states that energy cannot be created or destroyed, only changed in form. How does this apply to the Energy Can or roller coasters? As we learned in Newton's First Law of Motion, the roller coaster cars will continue to move until another force, in this case friction (wheels on the track and the coaster's brakes), acts upon them.

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