Newton’s first law of
motion states, “Every object continues in a state of rest or uniform speed in a
straight line unless acted on by a nonzero net force.” In other words, an
object will stay at rest until a force is acted upon it and an object will stay
in motion unless a force is acted upon it.” Theoretically, the construction of our mousetrap car seemed
pretty simple because the force of the mousetrap would cause our car to move
forward and according Newton’s first law to continue moving forward. However,
we had to keep in mind the FORCES that would act on our car to prevent it from
continuing in motion such as friction. We had to create a force that was larger
than the other forces acting on the car.
Newton’s
second law of motion states that force causes acceleration therefore force is
directly proportional to acceleration and acceleration is inversely
proportional to mass. (a=fnet/m). This law
was key in our construction of the car. If the force was larger then the
acceleration would be larger too. The more acceleration the car has the better
chance of the car going the distance of 5 meters and going faster than other
cars in the project. Also, we needed to keep a lighter frame and lighter axels
for the car so its mass would be less and it would have a greater acceleration.
Newton’s Third Law
states that every action has an equal and opposite reaction. Newton’s second
law can be explained in the formula (a=Fnet/m)which explains that acceleration is directly proportional to
force and indirectly proportional to mass. Newton’s Third Law can use this same
formula but you can write it in a different way: (F=ma).
The fact that every action has an equal and opposite reaction was important for
our car because we needed keep in mind that no matter what the ground would
pull down on the car and the car would pull up the ground with an equal and
opposite force, so the car needed to be strong. For example if this was our mouse trap car; Car F (10N) =mA the force would be
the same either way, but to control the distance and speed the car went we
would need to increase the acceleration rather than its mass.
The two frictions
present in this project were static and kinetic friction. Friction played a big
role in a project with its advantages as well as its disadvantages. When
constructing the car, we had to take into account the level of friction we
wanted the car to have on its wheels. At first, I thought it would make more
sense to have the least amount of friction on the wheels as possible because
according to Newton’s first law an object will stay in motion until a force is
acted upon it. (I thought friction would only be a disadvantage.) So, I thought
if there was no friction on the wheels there would be no force acting on our
car and it would keep moving. However, I soon realized that friction on the
wheels would be vital for our car to move. We put friction on the back wheels
so the car would be able to have traction to move across the floor. Otherwise
the wheels would just have been spinning without going anywhere. However, we
did not put any type of friction on the front wheels to allow the wheels to
spin freely and quickly. In this way friction was used to our advantage. Finding
the materials to use to create enough friction on the back wheels but not too
much was also a challenge. But after doing some research, wrapping cut up
balloons around the back wheels seemed to be the best solution.
We chose to do four
wheels for our mousetrap car because we thought four wheels would give our car
the best stability. At first, we planned to make the back wheels larger than
the front wheels, however, in the end we decided to use four discs. The back
wheels were CDs and the front wheels were DVDs. This was because the DVDs were
significantly lighter than CDs, so we wanted to have less mass on the front
axel so the wheels could move more quickly with a lighter mass whereas the back
wheels (attached to the back axel) needed to be heavier for the level of
friction and mass. Extremely large wheels seemed like a good idea because they
could cover a greater distance in a shorter amount of time and the small wheels
seemed like a good idea because they could move faster in a shorter amount of
time. This is why we originally had our car designed this way. However, we
found a moderate balance with the CDs and DVDs and decided to focus more on the
mass rather than the size. We wanted to keep the design simple and the equal
sized wheels made it easier to do so.
The conservation of
energy states that energy cannot be created or destroyed; it may be transformed
from one form into another; but the total amount of energy never changes. When
you think of a system, like a swinging pendulum, there is one thing that is
neither created nor destroyed, and that would be energy. The energy may change
form, for example, it may turn into heat, however, that does not mean the
energy is lost. Take a water dam for instance. The water behind a dam has
energy that may be used to power a generating plant below, where it will be
transformed to electric energy. The energy will then travel through wires to
homes where it can be used for everyday uses. Because we know energy does not
disappear or appear, it transforms, we can assume that kinetic and potential
energy can transform into one another. This is similar to our mousetrap car.
After considering this concept, we knew that the energy in the mousetrap car
would be the energy we would be working with no matter what. We could not
increase the energy or decrease the energy of the system. However, we could use
it more efficiently by storing enough potential energy in the car for the car
to transform into the kinetic energy allowing it to go the full 5m. The whole
system would have the same amount of energy in the beginning and in the end.
The length of our level
arm was a HUGE obstacle in the construction of our car. At first, we started
out with no level arm besides string, which we made twice the length of our
car. However, our car didn’t move. So a student at UNCA explained to us that
the longer the lever arm, the farther our car would go. So, we used a plastic
stick (part of a hanger) and attached it to our car. The first run with this
lever arm our car went 5m! After trying it again though, the car struggled to
go half the distance. It was frustrating and we thought maybe if we made the
lever arm longer it would help, but this just made the car topple over and it
even did a complete flip in one test run. Then we tried to balance our lever
arm so it was more centered. But again the lever arm was just not working for
us so we took it off and just used the string; this time the string was much
shorter. We also made our axels thinner. If we had constructed the lever arm in
a different way, the car may have gone 5m, however, it just did not work for
us. So our pulling force was simply the string coming forward with the
mousetrap device and pulling the back axel forward causing the back wheels to
spin forward.
Rotational velocity
is the number of complete rotations per time unit. We wanted our front wheels
to have a high rotational velocity meaning it would have more rotations per
time unit whereas the back wheels could have a greater tangential velocity. Tangential
velocity can also be called linear speed because it is something moving along a
circular path. The direction of motion is tangent to the circumference.
Tangential speed depends on the distance from the axis of rotation. Inertia is
the property of an object to resist change in motion dependant upon the mass.
This was important in the construction of our wheels because the larger the
wheels the greater distance these wheels would cover in a shorter amount of
time even though they would have a smaller rotational velocity. Rotational inertia is the property of an
object to resist changes in the spin of an object. It is dependant upon, not
the mass of each object, but where the mass is located on that object, how it
is distributed. It involves the distribution of mass and how far away it
is from the axis of rotation. If an object has a small amount of rotational
inertia, it is easier to spin compared to an object with a large amount of
rotational inertia, which is very difficult to spin. We set up the wheels
pretty close together because the less distance the faster the wheels would
go. We also had to make sure we
didn’t have the a lot of weight spread out on the car, this is why we used the
frame of the car to simply be the mousetrap because it would create a smaller
mass that was together creating less rotational inertia on the car. The less
rotational inertia our car had the better.
Work is the effort
exerted on something that will change its energy. Work equals force times
distance. [Work=Force X Distance] Work is measured in Joules. The force and distance must be
parallel to one another in order for there to be work done. We cannot calculate
the work being done on the spring because the spring is not parallel to the
distance the car travels. Potential energy is energy that is stored and held in
a stored state that has POTENTIAL of doing work. Potential energy is equal to
the combination (multiplied) of mass, gravity, and height.[Potential Energy= Mass X Gravity X Height] We cannot calculate the amount of
potential energy being done on the spring because we don’t know it’s mass or
its height. Also, we can’t measure don’t know the total energy of the system so
it’s not possible to calculate the potential energy. Kinetic energy is the energy of motion. Potential energy can
change into kinetic energy. The change in kinetic energy of a moving object
depends on the mass of the object as well as its speed. [Change in Kinetic Energy=1/2mass X velocity^2] Anything in motion has kinetic energy. According to the work
energy theorem, work equals change in kinetic energy. The change in kinetic
energy can’t be measure on the spring because we don’t have enough evidence of
the velocity of the spring itself. Acceleration is equal to speed times
distance, although we can measure the acceleration of the car, we cannot
measure the acceleration of the spring because we don’t know the distance it
traveled nor do we know the speed it traveled.
Our final design was
much different compared to our original design. Our original design is in the picture in the blog post before this one. Our final design had a much more simple layout. We learned the
smaller the axels and the smaller the mass of the system in general the more
functional our car turned out to be. Stability and simplicity were the main
goals we had to achieve in order for our car to work, which is why we made a frame
for the wheels on our final car.
The mousetrap car was
definitely a major struggle for our group partly because our car worked on
Friday and then over the weekend it somehow stopped working and forced us to
completely start over with the car. We struggled a lot with the lever arm because
according to concepts of physics we learned in the past, the longer lever arm
the farther the distance the car would go. However, with our car the longer the
lever arm the less our car functioned. So we had to take away the lever arm and
use string. Also, we struggled a lot with stability. The wheels of our car
seemed very shaky especially the front wheels. They kept sliding around causing
the car to run into the wall. So, we had to use part of a pen to prevent the
front wheels from moving but that took a lot of experimenting and sawing to
figure that piece of the puzzle out. Lastly, simplicity is what our design
struggled with. We were told that increasing the back axel would help the speed
of the car. We used a cork to wrap the string around it but this cork may have
been the foundation of our problems. The string let out too quickly so our car
couldn’t reach its full energy level. In the end, we had thinner axels (without
the cork) and no lever arm and our car went the required distance and it went fast.
If we were to do this
project again, I would definitely take the factors of simplicity and stability
into account and try to work with those more efficiently. Also, I think the
longer lever arm could really help the car go a farther distance, I just think
it needs to be constructed differently so the car is more stable. Also, the
axel issue seemed like the cork should be extremely helpful with the speed and
although it had a negative affect I would like to try and figure out a way to
use the thicker back axel and still have the string let out at an equal pace
instead of all at once. I think if we re did this project we could really make
outstanding cars.
