We were assigned to build a mousetrap car which could travel a distance of five meters. This project was very challenging, but at the end our car ended up going 5.21 seconds in five meters.
We hot glued to mouse trap to a wooden platform, and attached axels on the back and front by drilling holes and securing them with eye bolts. We fastened a colored pencil to the trap as our lever arm, and attached the string from the pencil to the back axel using zip ties. When the string is would around the back axel, the lever arm pulls the string forwards, and the back wheels move with it.
THE PHYSICS
àNewton’s First Law
Newton’s First
Law states that objects in motion will stay in motion and objects at rest stay
at rest until an unbalanced force acts upon it. According to this law, the car
would supposedly stay in motion forever, however friction acts on the wheels
causing it to stop eventually.
àNewton’s Second Law
Newton’s Second
Law states that acceleration is directly proportional to force, and is
indirectly proportional to mass. In terms of our car, if we had a larger force
causing it to move, it will have a larger acceleration. This also means that
the more mass the car has, the harder it will be to accelerate.
àNewton’s Third Law
Newton’s Third
Law states that every action has an equal and opposite reaction. In this case,
the action reaction pair is the car pushing the ground backwards, and the
ground pushing the car forwards
àFriction
Friction is
caused by weight and quality of the surface. The first time we rolled our car,
we noticed that the wheels weren’t gripping to the ground like they should have
been. In order to remedy this, we applied a few layers of electrical tape so
that the wheels would have more traction and would move better across the
floor. Although we wanted friction on our wheels, we didn’t want it on our
axel. We applied vaseline to the axel to get the string to pull off more easily
with less resistance. Both of these small changes related to friction helped
the car move more efficiently.
àWheel size
Originally, we
had two large wheels made of CD’s in the back, and two very small wheels in the
front. Even though all of the wheels moved well and were stable, the difference
in size of the two sets of wheels were an issue. Both sets of wheels had the
same rotational velocity, or number of revolutions per second. However, the
back wheels had a smaller tangential velocity than the front wheels, because
they are larger. The smaller front wheels had a larger tangential velocity in
order to cover a much larger distance to keep up with the back wheels. Since
the front wheels were spinning so much, they weren’t really taking the car
anywhere. We decided to replace the small wheels with larger ones, which solved
the problem and helped the car travel another 2.5 meters.
àLever arm
The lever arm
was attached to the mousetrap, and essentially is what made the car go. A
torque is factor that causes an object to rotate.
Torque=lever arm
x force
Essentially, we
want a smaller lever arm, because this will cause the force to be greater,
which will propel the car forward faster. Furthermore, the lever arm increases
the time and distance that the force is acting on the axel. However, I you have
very large wheels, you must have a longer lever arm since you will have a large
rotational inertia
àConservation of energy
It is important
to remember that energy can be neither created nor destroyed. It can however,
be converted into different types of energy such as kinetic (movement) and
potential (position) energy. When the car was at rest, it had a certain amount
of potential energy. Then when the car started speeding up, some of that
potential energy was gradually turned into kinetic energy. As the car slowed
down, some of its kinetic energy changed back to potential energy. However, the
amount of energy remained the same the whole time.
àWork calculation
Interestingly
enough, the car was actually not doing work before, during, or after if moved.
We know that work equals force times distance. But it is very important to remember
that force and distance must be in the same direction in order for work to be
done. The spring acting downwards on the car is not work, because the car moves
forwards.
REFLECTION
As stated
earlier, the only drastic design change was switching small wheels out for
larger ones. Smaller things like adjusting lever arm attachments, and dealing
with friction were other things we did to improve the car.
The biggest
problem with our car was when in the beginning, it would not go in a line, but
rather in a complete circle. This was because one of the back wheels wasn’t
touching the ground completely when it rolled. To fix this, we applied a few
layers of tape around the wheel to make it taller. We also added a little
weight to the side. These fixes corrected the turn, and we finally got the car
to move down the hallway.
If I were to do
this project again, I would research more and develop a solid plan before
beginning. We didn’t really know what we were doing at first, and more
organized planning would have benefited us greatly in the end.
