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Can you take the energy from a mousetrap and use it to power a car? Try it
This project results in a very simple mousetrap car. It probably won't go
very far or fast, but it'll help you learn the basics of how this type of car
works. Then you can try your hand at building a more complex car. See some ideas
at the end of the project.
Note: Mousetraps are dangerous! If one snaps back on your hand it could break
a finger. This project requires adult permission and supervision.
- Wooden snap-back mousetrap
- Duct tape
- 4 eye hooks
- Wooden dowel that fits inside the eye hooks
- Heavy cardboard
Large and small rubber bands
- Foam board (usually found at a craft store)
- Ruler or straight edge
- Utility knife
What to do:
- Have an adult help you use a utility knife to cut four wheels out of a
piece of foam board or corrugated cardboard. Make the back wheels about
double the diameter of the front wheels. (Use a compass to draw the circles,
or trace around a bowl or cup.)
- Give your wheels some traction by stretching large rubber bands around each wheel. For the small wheels you could
also try using a section of a balloon.
- If there are metal or plastic teeth on the mousetrap, remove them
carefully using a pair of pliers. Also remove the rod that is used to set
- Start building the base, or chassis, of the car by cutting a piece of
strong cardboard so that it is slightly bigger (about 1/2") than the mousetrap on every side. Use duct tape to attach the mousetrap to the base.
Don't cover up the spring in the
middle of the trap or the "snapper arm."
- Screw the eye hooks onto the bottom of the cardboard chassis, one in each corner. Use a ruler to make sure that the eye hooks are aligned with each other.
- Cut the wooden dowel so you have two pieces that are both about two
inches longer than the width of the chassis you have made. These will
serve as your axles that rotate the wheels. Stick the dowels through
the eye loops. Make sure that the axles are straight and that there is
room for them to spin in the eye hooks.
- Cut holes a little bit smaller than the dowel through the center of each
wheel, then attach the wheels to the base. Put the large wheels on the
back of the car, opposite the snapper arm. Wrap a small rubber band
around the axle on either side of each wheel so the wheels can't fall off.
- Tie a string very tightly to the snapper arm on the mouse trap. The
string should be long enough to just reach to the back axle.
- You may need someone to help you with this last step. Carefully
pull back the snapper arm until it reaches the other end of the trap.
Hold it in place while your helper wraps the string tightly around one side of the
axle. Holding the string tightly, set the car on the ground and
carefully let go of the trap - the string should be wound tight enough that
it holds the trap in place. Next, make sure everyone's hands are out of the
way and then let go of the string. The trap will snap forward, propelling
A set mousetrap is full of potential energy which, when released, is
converted to kinetic (motion) energy. The design of your car allowed that energy
to be transferred to the axle to make the wheels turn. When the trap snapped closed, it yanked the string forward. As the string was
pulled, friction between it and the axle caused the axle to rotate, spinning the
wheels and moving the car forward.
There are many different ways to build a mousetrap car. Your simple model
moves forward a few feet, but how could you design it to go longer distances? Or
how could you design it to go faster? Here are some things to think about:
- wheel-to-axle ratio. For distance cars, larger wheels are best.
Every time your axle turns one time, so do your wheels - if the wheels have
a much larger diameter than the axle, the car will go further on each turn
of the axle than it would if the wheels were smaller. It takes more force to
accelerate a car with a large wheel-to-axle ratio, so smaller wheels will
work better if you want your car to be fast.
- inertia. Newton's first law of motion states that objects at rest
tend to stay at rest, and objects in motion tend to stay in motion unless
acted on by an external force. Inertia is the tendency to resist changes in
motion, and the more inertia something has, the more force will be necessary
to change its state of motion. If your mousetrap car is very heavy, it will
require greater force to get it moving. To avoid too much inertia, think
about how you can build a lighter car.
- rate of energy release. If the energy from the mousetrap is
released quickly, your car will accelerate quickly and run faster. However,
it will also run out of energy sooner. If the energy from the mousetrap is
released slowly, the car will move slower, but be powered for a longer
distance. One way to try making the energy release slower is to lengthen the
lever arm by attaching something (pencil, dowel, etc.) to the snapper arm
and tying the string to the end of that. (This will give you a longer piece
of string than the one tied directly to the snapper arm.)
- friction. Analyze all the points of friction on your car, where
two substances rubbing together can slow the car down or bring it to a stop.
Think especially of how to reduce friction between your axle and the eye
hooks attaching them to the body of the car. Some friction is good, however
- the friction that enables the wheels to grip the floor is called
traction, and without it the force of the trap may make your wheels
"spin out" instead of propelling the car forward. The above procedure used
rubber bands to provide traction; can you think of a better way?
Other ideas for improving the car:
- make it more durable by using lightweight wood such as balsa or basswood
instead of cardboard.
- use CDs or records as the wheels.
- glue a small hook to the axle and connect the string to it with a small
loop, then wrap the string by turning the wheels in reverse.