The strength of the mousetrap is by fjzhangweiqun



     Everyone has seen a mousetrap. Those that have been caught

by a mousetrap know that it is powerful and fast. By transferring

that energy through levers, strings, and gears, it is possible to move

a small car. These mousetrap cars can be built for speed, distance,

or even power.

     By combining the simple machines of physics and

mathematics, I was able to build a mousetrap car. After building

the car, I was able to improve the design through trial and error so

that the car could propel itself twenty-seven feet.


     How do you get a machine designed to kill rodents to power

a vehicle? First, you have to start with a mousetrap. The only

power of a mousetrap is it’s spring. The lever arm is pulled back

along with the spring, storing energy. When something sets off the

trigger, the spring is released and the lever arm snaps. The basic

principle of a mousetrap car is to tie one end of a string to the lever

arm of a mousetrap, and the other end to the rear axle of a small

frame. The trap goes off, the spring is pulled, the axle and finally

the wheels are turned. Each of these steps can be adjusted to give

more speed or distance. I decided on a distance car.


     I constructed a mousetrap car out of two boards, PBC pipe,

brass tubing, two compact disks, a mousetrap, string, foam board,

and plenty of duct tape. First, I drilled a hole at each end of the

boards for the pipe. After placing the pipe in the holes, I taped the

mousetrap onto the frame. Then I placed the front axle through the

pipe. To get the CDs to fit on the axle, I had to wrap it in tape.

Once the CDs were on the axle, I wrapped the axle on each side of

the CDs with more tape to prevent them from wobbling and

detaching. Next, I attached the rear axle with one six-inch diameter

foam board wheel in between the two boards. Last but not least, I

tied two strings to the mousetrap arm, so I would be able to test

how each side of the axle operated when pulled.


     I conducted nineteen tests at this point, with the main intent

of how to get the car running consistently. I recorded the trials in a

chart. After I had completed those experiments, I decided an axle

hook was needed to run the car best (Balmer p. 28).

     To make the hook, I replaced the inside rear wheel with two

outside wheels of the same size and made of the same material.

Then I removed inside sections of those wheels to make them

lighter and easier to spin. I also replaced the two strings with one

long string. This allowed me to use a hook located in between the

two frame boards.

     Once I had realized how much of an improvement this was, I

decided to try and make a longer lever arm (Flamino). First I

clipped the original mousetrap arm. Then I cut a seven-inch long

brass tube to slide over the remaining lever arm. Because of

decrease in leverage the mousetrap was unable to operate at its best

capacity (Trials 2b-6b). In order to increase the torque to make the

trap work, I changed the wheel-to-axle ratio with tape (Balmer p.

28). After some fine-tuning I felt the car was at optimal


     During the course of my testing, I discovered different places

where energy was wasted. Bad wheels, extra weight, and friction

were all setbacks. Usually the wheels that I made were not

perfectly round. These wheels also had a center of gravity that

wasn’t on the axle. Therefore, when the car had stopped,

occasionally it would roll backward. Excess weight can ruin an

otherwise good car. With excess weight the car needs more torque

to pull itself, which can be obtained only by sacrificing distance.

Friction between the axle and the frame can be fixed by using ball

bearings or bushings. Ball bearings can be expensive, so I used

PBC pipe as bushings. The bushings are smoother than sanded

wood, but they still cause friction and cause the car to slow down.


     Now that I have a mousetrap power car that can travel over

twenty-five feet, I compared it to other cars. According to Balmer,

some distance vehicles can travel over 100 meters (333 feet),

which is more than twelve times further than mine will go (p.1). I

advise that anyone interested in building their own mousetrap car

should follow any good instructions that they find. Also, I learned

that, despite popular belief, duct tape cannot fix everything.


       Balmer, A. (1998). Mouse trap cars: The Secrets to Success. Austin, TX:

Armstrong Printing.

       Flamino, M. and McHale, K. (1996). Honors Physics Mouse Trap Car 7/11/01

Trial # Distance Changes                                                  Problems
1a     1 in       Attached right string to outside right                  Trap only snapped halfway
2a     8 ft       Attached right string to outside right around tape      Rolled back some
3a     2 ft       Left string to outside left around tape                 String came off early
4a     2 ft       Kept string tight during winding                        String came off early
5a     6 ft       Retried right side                                      String came off?
6a     2 ft       Attached string to axle                                 Stirng slipped off
                  Crossed string over itself
7a     0 in       Hooked string around axle                               String slipped off tape to axle
                                                                          Not enough torque to turn axle
8a     3 in       Retried                                                 String slipped off tape to axle
                                                                          Not enough torque to turn axle
9a     4 ft       Kept string on tape                                     Wheel ran over excess string
                                                                          Rear wheel wobbled
10a    4 ft       Tried to adjust wheel                                   Wheel went over string
11a    4 ft       Repostioned string                                      Wheel went over string
12a    9 ft       Wrapped left string around frame
13a    1 ft       Sanded wheel                                            Left string stopped the trap
14a    8 ft       Taped outside of wheel
15a    9 1/2 ft   Attached right string to inside right                   YES!!
16a    13 ft      Attached both strings to inside
17a    10 ft      Placed string ends near sticky tape (for easier rolling) Rolled back
18a    6 ft       Greased front wheels                                    Right string stuck to tape
19a    8 ft       Tried three rear wheels                                 Right string stuck to tape
Note: At this point I redesigned the vehicle, so trial numbers restart.

1b     17 ft      Replaced inside wheel with two outside wheels           Hit a bump
                  Placed small hook for string attachment
                  Replaced two strings with single long one
2b     0 ft       Made longer lever arm                                   Arm came off
                  Started in a different spot
3b     14 ft      Taped arm together                                      Arm pulled halfway
                                                                          Lacked torque to continue
4b     15 ft      Increased drive axle diameter with tape                 Still not enough torque
5b     8 ft       Increased axle diameter                                 Not enough torque
6b     27 ft      Increased axle diameter                                 Almost stopped twice
                  Replaced hook on drive axle                             String wasn't released from axle
7b     28 ft      Clipped hook                                            Almost stopped
8b     15 ft      Removed some excess weight                              Stopped at 15 ft
                                                                          Restarted after a small tap
9b     22 ft      Increased axle diameter                                 String wasn't released
                  Cut extra length from front axle                        Right rear wheel wobbled
10b    23 ft      Tightened wheel                                         I was lucky
11b    25 ft      Timed: 27.12 sec                                        String wasn't released
12b    18 ft      Retried                                                 Hit right wall
13b    26 ft      Observed string for problems                            String is too long to come off hook
14b    27 ft      Shortened string by tying knot


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