Voltage

Voltage is how we measure the difference in electric potential energy (∆PE). The two main ideas we covered are electric potential and potential difference.  Electric potential tells us how much work is necessary per unit of charge. Potential difference tells us how much total work is needed to move one charge to another point. The equation used for Voltage is V= ∆PE/q (q= one coulomb of charge). Example problem: If we were to move a charge from point A to point B and we put a number of joules of work in to the charge then we will recover the exact same number of joules in the charge if we move it back from point B to A. The joules of work are neither created nor destroyed, therefore the potential difference remains the same.

Mousetrap Car Challenge

Newtons first law and the mousetrap car: The mousetrap car stays idle until an unbalanced force acts on it (lever arm attached to mousetrap). The car will continue moving until an unbalanced force acts on it, such as a wall or friction.
Newtons second law and the mousetrap car: Acceleration is produced when a force acts on mass. When the mass of the mousetrap car is large more force will be needed to accelerate it, but with less mass means less force needed to accelerate the car, causing it to move faster.
Newtons third law and the mousetrap car: For every action there is an equal and opposite reaction (a=Fnet/m). This means that  acceleration is directly proportional to the net force and indirectly proportional to mass. In order for the mousetrap car to have a greater acceleration, the force acting on the mouse trap needed to be bigger. Also keep in mind that no matter how hard the wheels pushed down on the ground the ground pushed back up with an equal and opposite force.

The two types of friction present in this experiment are static and kinetic friction. A problem that I faced involving friction was the question on whether or not I should use balloon to tie around my CD's to create friction. I wanted my car to move as fast as possible and the thought of adding more friction to my wheels made me think that it would slow it down. I drew this conclusion based off of  newtons second law which states that the car will continue moving until an unbalanced force acts on it. However this assumption was wrong, because without the use of friction the wheels would then just spin in place and not move anywhere. By cutting out stripes from the middle of balloons and wrapping them around the CD's I was able to create enough friction for them to move.

In the beginning I planned on only using three whees, and having the back two wheels be larger than the front wheel, but in the end I chose to give my car four wheels because it seemed to be the best way to keep my car from drifting in other directions. The four wheels were CD's because they are light weight and easy to find. A key component that I added to my wheels was the use of cut out pieces of cardboard which I glued to both sides of the CD's. My two reasons behind doing this was so that I could drill a hole through it to stick the axle in, and because it increases the cars rotational velocity. By adding more mass to the wheels axis of rotation I decrease the wheels rotational inertia and increase it's rotational velocity.

The law of conservation of energy states that the total energy in an enclosed system cannot be changed; energy can neither be created nor destroyed, but can only change form. Knowing this we can conclude that the potential and kinetic energy can transform into one another. In relation to the mousetrap car I knew that the energy exerted from the mousetrap will always remain the same, for it all depended on how efficiently I used this energy. By storing the maximum amount of potential energy the car in turn will have a greater kinetic energy allowing it to go the 5 meters as fast as possible.

For my lever arm I attached a 6 inch pencil to the mousetrap and drilled a hole through it to tie a string around it. Before I decided that I wanted to use a pencil as my lever arm I did some research on it, because I knew that it was going to be a difficult obstacle. While researching I read about how the lever arm controls the cars acceleration, and if I wanted my car to move fast I needed a lever arm that wasn't too long because that would mean less pulling force. Having a long lever arm reduces the speed because it will bend under the tension of the mousetrap spring, thus wasting energy before the car begins to move. A pencil served to be the best possible solution for my lever arm because it is light weight and they don't bend easily. Also the pencil served as getting the most possible potential energy out of the vehicle because of its sturdy structure and large pulling force.

As stated earlier the rotational inertia and rotation velocity plays a key role in how fast the wheels spin. Since rotational velocity is the number of rotations per unit of time, I knew that in order for my car to move fast it had to have a greater rotational velocity. Rotational inertia is the property of an object to resist changes of spin. It is dependent on the mass and how it is distributed, for by having more mass closer to the axis of rotation means less rotational inertia and mass farther away from the axis means more rotational inertia. Tangential velocity is the speed in which a object moves on a circular path, it largely depends on the distance from the axis of rotation. By having larger wheels, they are capable to traveling more distance with less numbers of rotations.

We can't calculate the amount of work the spring does on the car because the force and the distance traveled are not parallel. We also can't calculate the potential energy that is stored in the spring because we don't know its mass or height (PE = mgh). Since we don't know the total energy of the system we also can't calculate the kinetic energy. Change in Kinetic energy = 1/2 mass x velocity and considering we don't know the exact velocity of the spring we can't solve for the kinetic energy.

My final design wasn't completely different from my original design. The only main difference between the two was that I had 3 wheels in my original design. What promoted this change was that I wasn't able to find a smaller wheel to put in the front so I just resolved to using 4 wheels. The only main problem that I encountered was that my string kept getting caught around the back axle, thus stopping my car before it reached the 5 meter mark. My resolution to this problem was cutting off 6 inches, which worked really well, because after doing this my car went 7 meters. If we were to do this project again I would use the mouse trap itself as the base, and I would use just string as my lever arm instead of a pencil.

Here is a labeled diagram of my final mousetrap car: My final times was 4:34 and I came in 4th place in my class.

Here is a video of my car in action: