My mouse trap car came in 3nd place with
a time of 3.25 seconds to travel 5 meters.
Newton’s first law states that an object in motion
will stay in motion unless acted on by an outside force and an object at rest
will stay at rest unless acted on by an outside force. This is the same for the
car; just replace the word object with car. A car in motion will stay in motion
unless acted on by an outside force and a car at rest will stay at rest unless
acted on by an outside force. Our challenge was to be able to apply the outside
force with the mousetrap.
Newton’s second law states that acceleration is
equal to force divided by mass. The car has a defined force that cannot change,
but the mass is still to be determined. My car was planned to have as little mass
as possible to increase the acceleration and there for the overall speed. This
was relatively successful as my car was light weight.
Newton’s third law states that for every action
there is an equal and opposite reaction. This is the cause of the car moving.
Below are the action—reaction pairs of the mouse trap car needed for it to
move.
The mousetrap pulls the string and the string pushes
the mousetrap
The string pulls the axel and the axel pulls the
string
The axel pushes the wheel and the wheel pushes the
axel
The wheel pushes the ground and the ground pushes
the wheels
The wheels of the car relies on friction, this is
good and bad. Good because the friction causes the wheels to move forward or
backwards or in whatever direction, but bad because too much friction would
cause the car to not be able to move at all. The challenge is to get the right
amount of friction, enough to get the wheels to grip the ground and move, but
little enough to not slow or waste the limited energy of the car.
The wheels of my car were CDs and they fit
appropriately. The wheels also are a challenge they cannot be to large or the
high rotational inertia will stop it from rotating but they must be large
enough to have a lever arm large enough to rotate the wheels. The lever arm for
the wheels is the distance from the axel to the edge of the wheel and must be
big enough to produce the torque required to turn the wheels. The CDs that I
used were very effective, they were the appropriate size. The limited force of
the mousetrap was able to help create the torque that the wheels need to
rotate.
The mousetrap is the force used to move the car and
it has stored energy in it. The mousetrap has potential energy that, when
released, becomes kinetic energy. This kinetic energy then drives the axels to
spin and the wheels to spin moving the car forward. There is limited energy
because of the law of the conservation of energy stating that the energy before
is equal to the energy after. The mousetrap only stores so much energy and that
is the total energy there is to propel the car forward.
Rotational inertia refers to who difficult it is to
make something rotate or stop rotating. This refers to the distribution of the
mass of the wheels and making sure that the rotational inertia is small enough
to have the wheels move forward and continue to move forward after the force
from the string has finished being applied. The speed that the wheels rotate
helps determine the speed that the car moves, the rotational velocity of the wheels
is different depending on the distance from the axis of rotation. The edge
rotates faster than the center, so the bigger the wheel the faster the
potential speed of the car. The tangential velocity is just a fancy name for
the speed of the car. This also depends on the speed of the rotation of the
edge of the wheel.
We cannot calculate the work done because no work
was done; the spring and the direction of the car are not parallel. To calculate
work the direction of the force and of the distance must be parallel. In this
case they are not. And because we cannot calculate the work we cannot calculate
the kinetic energy because of the change in kinetic energy is equal to the
work. If we cannot calculate the work we cannot calculate the kinetic energy.
To my original design was what I used to create my
car the only change I made was to the sting and axel. I detached the string
from the axel and attached sandpaper to it so that the string would stick to
it.
My only problem was that when I had the string
attached it would stop the axel from rotating and stop the car. I fixed this
problem by applying the explanation above.
If we were to do this project again I would plan to
work on it about the same way I did this project. I created the majority of the
car the first night and used the rest of the time to try and improve the design
changing little things to see if the car could go faster.
In my next building project I will do most
everything the same as this time because it worked well.
