Science Buddies: "Ask an Expert"

I have give the assigment to build a mousetrap car that goes a set distance and then stops. I have been thinking but i am un able to think of a way to do this that will stop the car complete with out having it to travel in any direction after it is ment to stop. All the ways i thought of would cause some back travel which is not allowed. Please help me.

Hi Shadow159753,

A simple search on http://www.google.com will list many sites with suggestions for this project. Here is one:

http://www.hypography.com/topics/mousetrapcar.cfm

I'm not sure what you mean by it cannot move in any direction, but if you're saying the car will be moving on an incline and cannot roll back after it stops, you could look into using non-round wheels. For instance, octagon shaped wheels along with the remaining spring force from the mousetrap may be enough to keep it in place. If you use a wheel with even fewer sides, such as a square, it will travel a shorter distance. Also, the larger the wheel diameter, the shorter the distance will also travel.

You'll need to experiment with tire shape and diameter to determine the size for the distance you need to go.

You can use popsicle sticks as a starting point and cut them down to size.

Hope that helps.

Thanks. I will try that.

I've done this kind of project. A simple string-brake works well (roll a string around the axle, when you go the set distance the string pulls tight and doesn't let the axle turn further). If you don't have a lot of friction on your wheels though, the string will stretch a little, behave like a spring or rubber band and sometimes cause your car to go backwards out of the "end zone". So a lot of people who used this approach also put a ratchet of some kind on the wheel to prevent the wheel from going backwards.

Large wheel sizes are easier to "aim" - the fewer revolutions of the wheel, the less likely the car will go somewhere unexpected from the direction in which you point it.