As Newtons first law says, an object in motion stays in motion unless acted on by an outside force. In the case of our mousetrap car, once it got going from the power of the mousetrap, it kept going. Our challenge here, was to make sure that there was no opposing force such as running out of string or having too much friction.
As Newtons second law states, acceleration=force/mass. Because a big force or mass causes big acceleration, it was beneficial for us to have a relatively heavy car. However, it could not be so heavy that the mouse trap did not provide enough power to propel the car.
As Newtons third law states, every action will have an equal and opposite reaction. In the case of the mouse trap car, the car pushed the ground back and the ground pushed the car foreword. This action and reaction pair is what caused the acceleration of the car.
Friction was a very important factor in the mousetrap car that both benefited and hindered us. The force of friction from the ground caused the torque on the wheel. To increase this friction (but not make it too much friction so that the car doesn't move) we added rubber bands to our wheels. In order for the axles to spin, there must be little to no friction in that area. Because of this we made our axles out of colored pencils which are smooth, attached them with smooth metal eye hooks, and stabilized them with smooth electrical tape. We also needed friction between the string and the axle so that it moved so we attached the string with hot glue.
The mousetrap cars work well if they are large because the bigger the wheels, the bigger the lever arm (distance from axle to edge of wheel), the bigger the torque. However, the wheels couldn't be too big because they have more rotational inertia which will make the wheels more difficult to turn. Because of this we used CDs which are light, have a good sized lever arm, but still moved easily.
Lever arm also applied to the mousetrap. Increasing the lever arm on the trap does not increase force but increases the amount of time that the force acts on the axle. Because of this increase in time and distance the force is decreased. We increased the lever arm to make the force act over a longer amount of time but we made it small enough so that there was still a large amount of force.
When the mousetrap is pulled back and set, potential energy is stored. It then gets converted into kinetic energy by being attached to the axle and making it spin.
Despite the power and energy, we can't calculate the amount of work the spring does on the car, the amount of potential and kinetic energy, or the force of the spring because the force and distance are not parallel.
Our first mousetrap car design was a tea box as a body with the mousetrap on top, colored pencil axles going through the body, mason jar top and CD wheels with rubber bands, and a string attached to the mousetrap, going through the body of the car and attached to the axle. This design failed because there was way to much friction on the axles and string, the axles were not parallel, the axles and wheels were not stable, the box was too light and flimsy, and the mason jar top wheels were bent and too small. In order to fix this, we added electrical tape to the places with too much friction, replaced the mason jar wheels with spools, old toy car wheels, and tape rolls and tried to adjust the axles to be straighter and more stable, added bolts and mason jar tops to make it heavier and we added wood to the box to make it more stable. The box, axles, and wheels were still to flimsy and there was still to much friction on the axles and string and between the wheels and box. We changed axles, wheels, and string countless times until we decided that the tea box would not work. We attached the mousetrap to a piece of wood and drilled eye hooks on either end. We put new colored pencils through these, attached CD wheels with rubber bands onto the axle with added support of Styrofoam (after trial and error with many other types of material) on either side to keep them straight. We added electrical tape between the eye hooks and the wheels so that the axle wouldn't move sideways but there was still very little friction. After that we made the string longer so that it wouldn't get stuck. The car was moving sideways because the wheels and axles were not completely straight so we added bolts and screws on the side to balance it out. That did not work so we took them off and changed the side that the lever arm was on. That still did not work so we reattached the wheels and their supports many times until they were very straight, messed around with the length on the string, and redid the eye hooks so that they were even. After 18 hours of work, our mousetrap car crossed the finish line.
If I were to do this project again I would make sure to measure everything very well as most of our problems came from adjustments because the axles or wheels weren't perfectly even. I would also make sure to have a very thought through and solid plan before starting as we jumped in to building too fast.
I would also make sure to continue to compromise, communicate and be flexible with both my partner and the car and continue to persevere no matter what.
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