Adam C. and Thomas E., The Broken Record
Mousetrap Car
Adam Cooke, Thomas Ehret
Mr. Boivin
SPH3UE, Grade 11 University Physics, Rockland District High School
Monday, November 19th, 2012
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Adam C. and Thomas E., The Broken Record
Introduction:
The purpose of this experiment is to build an originally designed vehicle powered solely
by the energy of one standard-sized mousetrap that will travel a distance of 10 meters.
Three of the most important things that need to be thought about when designing a
mousetrap car are Newton’s three laws. These rules are essential to have in mind when
thinking about the motion of a mousetrap car or anything that is in motion. Newton’s first law
is quite simple and it is referred to often as the ‘Principle of Inertia’ by physicists. The law is
basically broken up into two sections, one about objects at rest and the other about objects in
motion. The law states that an object that is not moving will remain stationary unless acted
upon by an unbalanced force. The motion part of the law is the same thing, stating that an
object in motion will have the same speed and direction unless acted upon by an unbalanced
force (Henderson, 2012). This is why the mousetrap is required for the car, the spring of the
mousetrap is an unbalanced force applied to the car to put it into motion.
Newton’s second law (See Figure 1) is slightly more complex however it can be
represented by an equation. The second law is stating that an object’s acceleration is
dependent on two variables. It is dependent on the net force acting on the object, which is
already known from the first law that an unbalanced force must be applied for an object at rest
to move. The other variable is the mass of the
object. This is unconsciously already known to
everybody because everybody knows that
something that is heavier will require more force
to move. Knowing these variables, an equation
was formed by Newton to represent this law: F =
ma (force is equal to mass times acceleration).
The third law that Newton came up with in
Figure 1. An example of Newton’s second of a
man pushing his car (Louviere, 2005).
Principia was also fairly simple but also important. It simply states that for every action, there is
an equal and opposite reaction. So if a man is pushing his car like Figure 1, he is exerting a force
on the car, but there is also an equal force being exerted on the man. Another example (see
Figure 2), is when air is released from a balloon because air pushes downward through the hole
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of the balloon, and at the same time the balloon is
pushed upwards, an equal reaction moving in the
opposite direction. Mathematically, this can be
represented by this statement, “When a first body
exerts a force F1 on a second body, the second body
simultaneously exerts a force F2 = −F1 on the first
body. This means that F1 and F2 are equal in
magnitude and opposite in direction (Anonymous,
Newton's Laws of Motion, 2012)”.
In the experiment the goal is to design, build
Figure 2. A classic example of
Newton’s third law in action
(Anonymous, Newton's Laws of
Motion, 2012).
and test different vehicles that are powered by a single standard sized mousetrap car. The goal
is also to try and get the car to travel a distance of 10 meters.
Design Strategy:
Our original idea for the design was a four CD wheeled car with wooden axles and a
Styrofoam body (See Figure 3.). We figured this design would function perfectly fine once we
acquired more pieces like the rod for the
snapper, the eye hooks to hold the axle,
and possibly different front wheels that
were smaller. By the third day, we had
game cube disks to use as our front
wheels, the eye hooks, shish kabob sticks
for new axles, a yoyo string, and the rod to
attach to the snapper (See Figure 4.) The
thinking behind these new parts was based
on performance obviously. The smaller
Figure 3. The pieces of the original design
plan.
wheels in the front would allow for less
friction, and more momentum making for more speed. The rod was intended to increase the
length of the string and the amount that the snapper would turn the axle. The string from the
yoyo seemed liked a great thing to use because of its original function and the way we would
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apply it to our mousetrap car. Lastly, the
shish kabob sticks were put into play when
we realized our eye hooks that were not
complete circles would not work because
the axles would just slip out. We were
aware that we had eye hooks that had a
complete circle at the house and the shish
kabob sticks would make perfect axles for
these eye hooks. There was not much
assembling on this day, but a lot of
planning and ideas being made.
Figure 4. The third day’s design parts now
including shish kabob sticks, a yoyo string,
Game-cube disks, and a plastic rod.
On the same day, we came to realization that the idea would simply not work, and if it
did, it would not be easy to complete and execute. This is when we basically trashed the design
and began working on our two wheel record design (See Figure 5.). The start of the design was
extremely simple consisting of a bolt as the axle, the two records held in place by nuts and
washers and then the mousetrap hanging by eyehooks from the axle. This design was inspired
by a similar one that we found online. This plan seemed like the way to go because of the
simplicity, light weight, and efficiency.
Having only two wheels, we knew that
at full momentum, it would roll quite a
distance. It seemed much better than
the common three and four wheel
designs because there was not very
much to worry about in terms of forces
acting against it and other structural
problems. It turned out to be slightly
flawed at the beginning because the
string just slipped out of the axle
Figure 5. The beginning of the two wheel
record design.
instead of pulling and turning it.
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This is when we taped the axle
with electric tape where the string would
be wrapping around (See Figure 6.).
Even after this, the string would not
wrap itself around the axle properly. We
resorted to wrapping tape around the
axle facing outward so the string would
stick. It proved to work in the hallway at
the house but at school, the string never
detached itself from the tape so it rewrapped itself, then stopped and started
rolling the opposite direction. This is
Figure 6. Very similar to (Figure 5.) but with
added tape in places like the axle where the
string is wrapped.
because the string was slightly too long and the momentum of the car was not strong enough
for the string to come off of the tape. We then
took the tape off, and added a piece of a tie
wrap that was slightly over the axle so it left a
small hole that we would feed the string
through (See Figure 7.). After many attempts,
we found a way to wrap the string so that the
design would work. This final design went a
distance of 8.7 meters. That run did not get
video-taped but here is a run that did:
MousetrapVid.MOV
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Figure 7. The final product that had the
piece of tie-wrap allowing for a hole to
slip the fishing line through.
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Results and Calculations:
After all of our adjustments, our mousetrap car traveled a grand total of 8.7 meters on
our last attempt almost reaching the goal of 10 meters. Overall we believe that this was a good
result for our car considering the challenges we faced during the designing process and on the
first day of competition. However, compared to other groups’ results we were not in the top
groups in terms of how far their cars went. The highest total from the competition was 25.3
meters, much more than our measly 8.7. Although it should be noted that the design that went
the farthest was very similar to ours and the same concept as our design.
Calculations: ∆𝑑 = 8.7𝑚
∆𝑡 = 22𝑠
𝑚 = 360𝑔 = 0.360𝑘𝑔
∆𝑑
∆𝑡
8.7𝑚
𝑣=
22𝑠
0.396𝑚
𝑣=
𝑠
𝑊
𝑃=
∆𝑡
0.06𝐽
𝑃=
22𝑠
𝑣=
𝑃 = 0.003
𝑊 = 𝐹∆𝑑
1
𝐸𝑘 = 2 𝑚𝑣 2
1
𝐹 = 𝑚𝑎⃑
𝐸𝑘 = 2 (0.360𝑘𝑔)(0.396)2
𝑊 = 𝑚𝑎⃑∆𝑑
𝑣𝑓 − 𝑣𝑖
𝑎⃑ =
∆𝑡
0.396 − 0
𝑎⃑ =
22𝑠
𝐸𝑘 = 0.028
𝑎⃑ = 0.018𝑚/𝑠 2
𝑊 = 0.360𝑘𝑔(0.018)(8.7𝑚)
𝑊 =0.06J
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Conclusions:
After the conduction of this experiment, the mousetrap car “The Broken Record”,
achieved a maximum distance of 8.7 meters falling just shy of the 10 meter goal that was
previously set. Again, although this result was not quite what we had originally hoped it was
quite close to our original goal. One of our best accomplishments during the process of
designing and competing was the fact that when something went wrong, we immediately knew
what needed to be fixed. For example when we encountered the problem with the string on
the first day of competition, we instantly knew that it was because the string was wrapping
itself back around the axle and we fixed that problem and got a longer distance. Our first major
setback was when we had a solid design but our eye hooks did not hold our axles in place which
killed the design. In our second (and final) design, our setback as earlier stated was that the
string we used kept wrapping back around the axle and luckily we were able to solve this.
When thinking about the physics of this mousetrap car, there were some things that we
really did well in and other aspects that we definitely could have improved. In terms of friction,
we actually limited friction very successfully by using the records as our wheels. There was
definitely very little friction because in testing and competition, the car would roll quite a
distance further after the force from the spring was diminished. This was also important
because when considering the principle of inertia, we needed a force to put the mousetrap in
motion and remain in motion and in order for us to accomplish this; we needed as little force of
friction as possible to maximize the force applied by the mousetrap spring. Overall the
kinematics and forces of the car were well thought of and executed, just the string that
wrapped around the axle created an unbalanced force which stopped its motion. However
overall we are pleased with the result of 8.7 meters.
Questions:
1. What are the two types of friction that affect the performance of your vehicle?
The two types of friction that affect the performance were static and rolling friction. The static
friction is present because a force was required to overcome the static friction and start
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moving. The rolling friction is the friction that occurred between the floor and the wheels when
the car was in motion.
2. What problems related to the friction did you encounter and how did you solve them?
Well one of the problems encountered with the friction of the mousetrap car is the wheels. It is
inevitable that there will be friction with the wheels so we limited it as much as possible by
using records because they are very thin, lightweight, and have a very large radius. Another
problem is the friction between the axle and the eye hooks holding the mousetrap onto the
axle. Once again, there will be friction there no matter what so we made sure we took very light
and smooth metal eye hooks.
3. What factors did you take into account to decide the number of wheels you chose in your
design?
When deciding the amount of wheels to use, we decided on 2 because we figured that the
fewer wheels there were, the better chance the car would have of going straight. This is
because there would be fewer wheels to worry about being perfectly in line with each other.
We also considered the axles being perfectly parallel and came to conclusion that it would save
a lot of time to not have to do so many measurements.
4. What kind of wheels did you use in each axle? What is the effect of using large or small
wheels?
On our sole axle, we decided to use records as wheels. This was decided for a couple reasons;
one being that the mousetrap would have to hang from the axle because of the individual axle
design, so the mousetrap cannot touch the floor. Another reason is that the axle will turn the
same amount but with the greater circumference of the wheels, it will cover much more
ground.
5. Explain how Newton’s first, second and third laws apply to the performance of your
vehicle.
Newton’s first has a huge part of the performance of the vehicle. The unbalanced force acting
on the stationary car should be as big as possible or the car should require the smallest amount
of force possible for it to become in motion and allow for the best performance possible. Also,
the unbalanced forces acting on the car when it is in motion should be as limited as possible.
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This would include making the car so it does not have very much friction and making it
aerodynamic.
6. Discuss the effect of the length of the lever arm in the pulling force of your vehicle.
Our two wheel design involving the hanging of the mousetrap on the axle made it so that we
could not extend our lever with a rod of some sort like many other groups did. Our lever was
technically the snapper on the mousetrap which did not make for a lot of string to pull on
between the axle and the wound up mousetrap. Though, the design is meant for the car to hit a
high speed very quickly and then cruise for a long distance.
7. How is the balance of a wheel, around its center, related to the vehicles performance?
The balance is extremely important for the performance of the vehicle because if any wheel in
the design is unbalanced, it can cause the vehicle to go completely off course or in circles. This
includes any design no matter how many wheels it has though usually between 2 and 4. We are
aware of this because it was one of the problems that we came across during the process of
constructing the vehicle. This problem can be fixed (At least in our case) by tightening the nuts
holding the wheel in place with 2 wrenches.
8. How does the distribution of weight of the vehicle affect the traction of the wheels?
The distribution of weight affects the traction of the wheels because applying force onto the
wheels will create better traction between it and the ground. If a wheel is somewhat loosely
hanging from the design, it will have very little effect when the vehicle is accelerating or
becomes in motion. It was simple to distribute the weight in a two wheel design because it
automatically gets distributed evenly if the wheels are aligned properly and the measurements
of the design are done correctly.
9. Discuss the major problems encountered in the performance of your vehicle and what
you did to solve them.
One of the major problems that we encountered in the design process was the string and how
we would wrap it around the axle. When wound up, the string would always come loose
without even turning the axle no matter what kind of string we used which became a huge
problem. Originally, we used tape with sticky side facing outward so that the string would not
come undone until it completely unwrapped itself. Though, the string would never come
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undone so it would rewrap itself and then eventually stop and go the opposite direction. We
then decided to change the string to fishing line, take the tape of and make a hole between a
portion of a tie wrap and the axle. We would then slide the string through the hole which would
be small enough to allow the string to wrap itself around the axle and actually turn it. Originally,
it did not work but eventually we found a strategic way to wrap it. Another problem we
encountered was the nonlinear path that the car would take. It had a tendency to curve pretty
severely sometimes and after some brainstorming, the best solution was to tighten the nuts on
either side of each wheel with 2 wrenches.
Selected References:
Anonymous. (2012). Newton's Laws of Motion. Retrieved November 17, 2012, from
TutorVista.com: http://physics.tutorvista.com/motion/newton-s-laws-of-motion.html
Anonymous. (2012). Newton's Laws of Motion. Retrieved November 18, 2012, from Wikipedia:
http://en.wikipedia.org/wiki/Newton's_laws_of_motion
Henderson, T. (2012). Newton's First Law of Motion. Retrieved November 17, 2012, from The
Physics Classroom: http://www.physicsclassroom.com/class/newtlaws/u2l1a.cfm
Louviere, G. (2005, October 8). Second Law of Motion. Retrieved November 17, 2012, from
Georgia Louviere's Website:
http://teachertech.rice.edu/Participants/louviere/Newton/law2.html
Appendix:
Journal/ Log
Day 1: Tuesday, November 6th, 2012
On the first day we worked on it, we wanted to establish what materials we would need
and what our final product would look like. In terms of materials, we looked around the house
for what we had and wrote down the things we did not have on a note as a reminder. Some of
the materials we did find around the house were the Styrofoam base, the wooden axles, the
eye hooks to hold the axles, the CDs for the wheels, and electrical tape (See Figure 3.) On the
note for the items we needed to pick up or buy, there were Game-cube game disks for the front
wheels, string or fishing line, and a rod to extend the length of the string to increase the
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amount of time it would pull for. The original design idea was to have the Styrofoam base with
the mousetrap on top, with eye hooks holding wooden stick axles which have two CDs as the
wheels on the back, and two Game-cube game disks (smaller) as the wheels on the front. Then
the rod would be attached to the snapper on the mousetrap. After this day, we were not aware
of any problems that we would encounter. The cost of materials on this day was nothing
because we simply used items that were around the house.
Day 2: Wednesday, November 7th, 2012
The only things that we did this day for the project were buying the rod ($1.99) and the
Game-cube games (Free). We found a yoyo around the house and figured that the string might
be useful.
Day 3: Thursday, November 8th, 2012
On day three, we came to conclusion that our design was a complete flop. The eye
hooks would not work because they were not complete circles and the axles would just slip out.
Our first solution to this problem was to find much more narrow wooden axles and use smaller
eye hooks that had complete circles (See Figure 4.). Once we realized that we could not find
these eye hooks, we threw out the blue prints, and began making the 2-wheel-record design.
This design consists of a single axle (bolt) in which the mouse trap is swinging from in the
middle and has two records on either side held in place by nuts and washers (See Figure 5.).
There is no rod needed in this design, simply the string tied to the mousetrap snapper and then
wrapped around the axle. The records, bolt, nuts, washers, and fishing line were found around
the house so the cost was nothing. Originally, the fishing line was used as the string, but it
would not wrap around and pull the axle properly when wound up. We called an audible and
used the yoyo string instead (See Figure 6.). We wrapped a piece of tape around the axle with
the sticky side facing out so that the string could actually wrap around.
Day 4: Friday, November 9th, 2012
Today was the official race day. Our first run with the car only went 5.34m because the
string wrapped itself back around the axle and forced the car to stop and roll backwards a bit.
We immediately removed the outward facing tape and put on a piece of a tie-wrap. We then
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slid the string between the tie-wrap and the axle so the string would be able to wrap around
but slide out when the string unwrapped itself. We tried it again and the string was too thick to
come out of the hole. Being there not very much time left in the period, we decided that on
Monday, we would quickly replace the string with fishing line (See Figure 7.)
Day 5: Monday, November 12th, 2012
On this day, we executed the replacement of the yoyo string and fishing line and got a
final best distance of 8.7m. The only problem that occurred on this day was the difficulty to
properly and strategically wrap the string around.
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