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the physics of a mousetrap car



Last week I began building a mousetrap car with a friend of mine who was given the assignment as an extra credit assignment in their physics class. Their assignment is to build a car whose sole source of energy is a mousetrap. Whoever's car goes the farthest wins. While doing my research I found a few ideas centered around physics that appeared most important to the success of our car.

large wheel to axel ratio

Due to the small size of a mousetrap we only have the ability to rotate an axle a small number of times. To make the car travel as far as possible and to turn the few rotations we have into as much distance as possible we can make the wheels significantly larger then the axle. In this way every full rotation of the axle gives us a significant amount of distance.

Have Some Friction, But Only Enough

Whenever a problem involves using energy as efficiently as possible you will want to decrease friction as much as possible however in this problem we have to be sure we do not remove friction too much. In the case of our back wheels we are going to need a certain amount of friction to ensure that the wheels turn. The force friction between the wheels and the ground will provide a torque to drive our car forward. If there is not enough friction on the wheels they may began to slip on the floor. If this happens our potential energy is being turned into the rotational motion of the wheels but not the translational motion of the car. In other words, we are wasting our precess energy.

Long Fulcrum

Increasing the length of our fulcrum will have an effect similar to that of our large wheels. By increasing the fulcrum we can increase the total distance that we can turn the axle. The Fulcrum is the radius of a circle created by its rotation. If we increase is length we increase the circumference of that that circle and therefore increase the distance that we can pull the axle over. This in turn leads to more rotations of the axle and more rotations of our wheels giving us more distance.

Other then this a lot of it is simply tinkering around with your design until you have maximized your distance with the tools and materials you have. Try it out and see what you think.


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