Mousetrap Car Review

We recently finished our Mousetrap Car project.   It was full of physics, power tools, blood, sweat, and tears.  First, we'll go into the Physics concepts in the project.

Friction is a very important part of this project.  Friction is effected by two things: Weight and
Different Surfaces. If the Friction is too small, there will not be enough torque. Too much Friction, there will be too much torque.

All three of Newton's Laws are represented in this project.

Newton's First Law states that an object at rest will stay at rest, while an object in motion will stay in motion, unless acted upon by an outside force.  This is seen in the project in that the car, if in motion, will stay in motion unless a force pushed it backward.  In this case, the outward force is friction.

Newton's Second Law states that Force is equal to Acceleration x Mass.  This can be rephrased to Acceleration= Force/Mass.  In the car, the force, or the snap of the mousetrap, causes the acceleration.  The bigger the force, the greater the acceleration.  However, too much mass will lower the acceleration.

Newton's Third Law states that for every action, there is an equal and opposite reaction. For the mousetrap car to work, the car pushes the ground back and the ground pushes the car forward.  This is the very force that allows the car to move.

Energy wise, pulling the trap back creates Elastic Potential Energy. When the trap is released, the PE is converted to Kinetic Energy, which causes the axel to turn.  Storing energy in the spring and using it's torque to create a force will cause the axel to move.  This is because the force is perpendicular to the axel, and thus the direction. It is important to note that the amount of energy in the car remains constant throughout the whole expedition. 

By adding a lever arm. we do not increase the force- rather, the lever arm increases the time and distance that the Force is acting on the axel.

THE CAR
Below is a video of our car.  It completed the required distance of 5 meters, and came in 3rd place with a time of 3.77 seconds.
 
With the picture below, we can see how these physics concepts apply on the actual car we made.

Starting with the wheels, you can see that all four wheels have electrical tape around them. This is to create friction.  Although in other places in the car, Friction was our "worst enemy",  Friction between the wheels and the ground is necessary for the car to move.  Also something to consider is the size of the wheels.  All wheel need torque (force x lever arm) to turn.  Larger wheels have a big lever arm, creating a big torque.  Larger wheels will also have a smaller rotational velocity.  Small wheels, on the other hand, have a smaller lever arm and thus a smaller torque. They also have a high rotational velocity.  However, all of the wheels of the car will have the same tangential velocity. 

Next, the frame.  A light frame is necessary, just as we talked about above, in Newton's Second Law. A frame too heavy means that the car cannot accelerate.

By using the formula velocity= distance/time, we can see what the average velocity of our car was.  It went 5 meters in 3.77 seconds, meaning that its average velocity was 1.326 m/s.   An important thing to note, however, is the we aren't able to find the amount of work done by the spring on the car.  This is because the spring's force and direction are perpendicular, meaning that no work is done.  Without force, we are unable to find the Change in Kinetic Energy, or the Potential Energy stored in the spring.  We also cannot calculate the amount of force exerted on the car to accelerate it, because again, the force and direction are not parallel.

REFLECTION

This was one of the more frustrating projects I have ever completed.   However is was the difficulty that made the completion of our car even more satisfying.   Our design varied greatly throughout the process.  The most notable changes are those made with our frame and our wheels.

The wheel change occurred after I tried to set our car off and it flipped over completely.  This was because our back wheels were significantly larger than our front. We rectified this issue by changing the back wheels from larger wooden disks to CDs.  This allowed for a more balanced car.

The most drastic change was the shift we made just two days before the car was due.  We noticed that our axles were crooked due to the way that they were attached to the base of the mousetrap.  We did some research, and realized that we should increase the distance of the wheels and also create a hole for the axles, allowing them to turn more easily. This turned out to be the best decision we could have made.   

Aside from the structural issues mentioned above, we had major problems getting our car to move by itself.  Our vision of a lever arm attached to a string which would wrap around the back axle never changed, but we had to make lots of little adjustments.  This problem greatly hindered the proformance of our car initially, but we were able to rectify this by lengthening the lever arm and shortening the string.  This allowed our car to have enough power to complete the five meters.

To make our car go faster, I would have done a number of things.  First, I would have made all of our axles slightly smaller.  This would decrease the amount of friction between the axle and the frame, allowing for more speed.  I also would have made a lighter frame, because as we stated above, a heavy frame decreases the acceleration.

If we were to do this project again, I would do more preliminary research before starting.  Niara and I had a lot of confidence, and that made us think that we could complete the project without any resources besides ourselves.  I think our process would have gone much more smoothly had we consulted books or websites.