Newton's first law
object in motion stays in motion
Using one wheel in the front helped us have less rotational inertia and less mass. The two wheels in the back are CDs covered with balloons. The CDs serve to lessen the mass as well. Bottle caps are glued to both sides of the cd to increase stability so that the car will stay straight. The balloons serve as friction so that the car can move forward. The "body" is made of two slabs of the lightest wood we could find. To save mass, we chose to connect the mouse trap directly to the outside wooden frame. The axels are brass rods drilled through the wood. The front wheel was made up of two bottle caps and a wheel from a toy car. Paper was inserted inside the toy car wheel to make it have less friction against the brass rod. The bottle caps glued to both sides of the car wheel were originally used to keep the car wheel from tottering and therefore steering the car straight. The front wheel was not glued to the rod- so that it would freely spin. The back wheels were directly glued to the brass rod on the oustide of the wood, however the brass rod would still spin once the mouse trap was let go. We used fishing line, the strongest and smoothest material, to lesson the friction. We needed more tangential velocity so that when the string spins off of the back axel, it will travel faster-- so we added a glue stick with a drilled center and placed it in the middle of the brass rod. The easiest and lightest way to attach the fishing line to the rod was to staple it into the glue stick. We needed something that would hold fast to the rod and the glue stick worked perfectly. The lever arm was a pencil duck taped to the mouse trap. It was light and therefore lessened the mass while also raising the tangential velocity so that the car would be able to cross the 5 meter mark.
Newton's first law states that objects in motion stay in motion unless acted upon by an outside force. This statement refers to the whole purpose of the car. We wanted to reduce the activity of outside forces on the car so that it would keep moving to pass the five meter mark. In order to do this, we lessened the friction in the front wheels as much as possible and avoided putting glue between the hole drilled in to the wood on the back of the car and the inside bottle cap holding the CDs in place. We had to glue the CDs on the rod without letting the glue leak from the bottle caps and touch the nearby wood where the axel needed to rotate. The holes drilled into the wood were drilled smoothly so that the brass axel would not catch them and therefore add friction to the system. However the front wheel served as a main problem. The car does need some friction, but it does not need much. The front wheel had glue on the sides where the bottle caps were attached, therefore making the ride a bumpy one and adding friction between the wheel and the floor.
Newton's third Law states that every action has an equal but opposite reaction. The back wheels would push down on the ground when the mouse trap is set off, however since the reaction is equal and opposite the ground must push on the wheels. So how does the car go anywhere? Its the same as the horse and buggy problem. The balloons are the hooves of the horse. They add friction so that the car may move. The two types of friction are static friction (only when the car is at rest) and kinetic friction (friction that the car has when moving). We need static friction so that the back wheels can stabilize and push down on the ground. However Kinetic friction must be avoided as much as possible.
The front wheels and the back wheels had different rotational inertia. However the tangential velocity was the same because they covered the same distance in the same amount of time. We needed the rotational inertia to be different so that the back wheels would have more and therefore create friction so that the car would be able to move forward. We wanted the front wheels to move freely with less rotational inertia so that is why we chose smaller wheels.
The lever arm was the size of a normal pencil, probably six inches. The longer the lever arm, the higher the torque and the more output power there is. So when we first tried the car without a lever arm the car did not have alot of power. But by adding the lever arm we increased the torque and therefore the car went farther and had more power.
The less friction on the car the more conservation of momentum we have. That is why reducing the friction of the car is so important. Not all machines are very efficient, so if the mouse trap car is expelling sound, light, or heat... that is energy that the car has released and put into moving the car forward.
If we wanted to calculate the amount of work the spring does on the car, we would need to know the force. Since we dont know the force we cannot find the work and if we cannot find the work then we certainly cannot find the Kinetic energy the car used because work = change in KE. The change in KE is equal to the change in PE, Therefore we cannot find any of them. We cannot find the force in the first place because force = mass x gravity.. And we cannot measure the mass so therefore we cannot find the force.
Reflection:
We faced problems with the height of the front wheels, making sure
that the axel is not crooked, and that the drilled holes are aligned. We faced
problems with making sure the front wheel is stable. Adding bottle caps to all
of the wheels was a deviation from the original design. But they were used for
stability purposes and to create a way for the axel to rotate freely. I feel
like the main problem was having foresight to find how to create the next step
for the car. Another problem was the front wheels, we had to attach them
several times and then that created friction so we ended up just letting them
ride along next to the car tire and peeling off the glue. I would not want to
do this project again; if I had to I would make things neater and I would use
smaller wheels, less glue, and lighter wood.
