THE MOUSETRAP CAR
SCIENCE ACTIVITIES
Page
What Is A Mousetrap Car and How Does It Work?
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Builder’s Tips
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How To Build A Mousetrap Car
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SCIENCE ACTIVITY 1: Simple Machines
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SCIENCE ACTIVITY 2: Calculating Velocity
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SCIENCE ACTIVITY 3: Relating Circumference and Distance
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SCIENCE ACTIVITY 4: Vehicle Mass and Distance Relationship
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Engineering Challenges I & II
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1
What is a mousetrap car and how does it work?
A mouse trap-powered racer is a vehicle that is powered by the energy of a wound-up
mousetrap's spring. The most basic design is to tie one end of a string to the tip of a
mousetrap's snapper arm and then the other end of the string has a loop that is designed to
"catch" a hook that is glued to a drive axle. Once the loop is placed over the axle hook, the
string is wound around the drive axle by turning the wheels in the opposite direction to the
vehicle intended motion. As the string is wound around the axle by the turning of the wheels,
the snapper's lever arm is pulled closer to the drive axle causing the mousetrap's spring to
"wind-up" and store energy. When the drive wheels are released, the string is pulled off the
drive axle by the mousetrap causing the wheels to rotate.
How do you build a mousetrap Car?
There is no one "right way" to build a mousetrap powered vehicle. The best approach is to
apply your best understanding of the laws of physics without over exaggerating any one
concept to your design. To build the "perfect" mousetrap car you must try and find a
harmonious balance between all the elements and variable that will affect a mousetrap
vehicles performance. Do not be fooled into thinking there is only one way to build a winning
mouse trap racer, we have been building mousetrap cars for over 15 years and our designs
continue to change; one year everyone is designing cars with huge big wheels and the next
year everyone has moved on to pulley systems. Be willing to try something original, it might be
the next "thing". The first step to making a good mousetrap powered car is simple, put
something together and find out how it works, it may not be pretty but it is a start. Once you
have something working you can begin to isolate the variables that are affecting the
performance and learn to adjust to improve your results. Building mousetrap cars is a simple
process of design engineering, you build, you test and experiment, you change, and you do it
all over again.
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Builder’s Tips
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Safety
With any spring-loaded or spring-powered device, it is important to keep fingers out of
harm’s way. Children should be aware of the fact that the spring can pinch.
Exercise caution when children are using cutting tools like the X-ACTO knife. Children
should be monitored closely. Adults may prefer to do some of the cutting for younger
children, particularly on smaller items.
Helpful Hints
Liquid soap can be used to “grease” the axles when rubber spacers are difficult to put on or
remove.
Use a 1/8 inch drill bit to ream out the holes in the rubber spacers.
Keep the string taut when winding it around the drive axle.
The string should be just long enough to reach the drive axle. If it is too long it will tangle
around the drive axle and stop the vehicle.
Place a band around the drive wheels to give the wheels added traction.
Overcome friction in moving parts by adding graphite powder. The most common
application is between the axle and the frame in order to reduce the rubbing friction. Also
place a little on the mousetrap's spring to save even more energy.
Add masking tape to the drive axle to increase its diameter, thereby increasing torque.
Troubleshooting
Mousetrap vehicles can have problems with steering. Using a smooth and level course for
racing vehicles will help keep the cars moving along a straight path.
Another hindrance to straight steering could be wobbly wheels. Check the wheel spacers –
you may want to change the spacers to ones that are tighter.
You will also want to make sure that the wheels are aligned. Before assembling the vehicle,
place the side rails together and check to see how well the predrilled axle holes line up.
You may want to turn the side rails around to make the best match possible for the holes. If
you are drilling your own axle holes, drill through both side rails at the same time and make
sure to keep the drill as straight as possible. After the vehicle has been assembled, the best
advice for misaligned wheels is to maximize the path of the vehicle.
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How to Build a Mousetrap Car
1. Make the frame. Center the deck between the two side rails, and glue it in place.
2. Place the six-inch axle rods in the frame’s predrilled axle holes. Place a metal thrust washer
and a black spacer on each side of each axle.
3. Center the axles in the frame.
4. Place the CD spacers into the center of the wheels.
5. Slide the wheels onto the axles.
6. Locate the mousetrap and use needle-nose pliers or wire cutters to cut the trap’s snapper
arm. Cut the arm in the corner above the place where the trap’s spring presses against the
arm.
7. Remove the snapper arm and the locking bar.
8. Use pliers to straighten the non-loop end of the locking bar. Slide the locking bar into one
end of the brass lever arm and use super glue to secure.
9. Slide the other end of the lever arm over the remaining section of the snapper arm on the
mousetrap. Make sure that the lever arm slides under the trap’s spring arm.
10. Position the mousetrap on the deck of the vehicle so that the lever arm is in the center of
the deck. The lever arm is pointing toward the front of the trap (and the front of the vehicle)
when the spring is not under tension.
11. Keeping the lever arm aligned with the center of the deck, move the trap so that the rear of
the trap is 10 ¼ inches from the rear axle. The rear axle is the drive axle. Remember the
lever arm is pointing toward the front of the trap and the vehicle.
12. Superglue the trap into position.
13. Tighten the ziplock around the center of the drive axle, and trim the excess flush with the
clasp.
14. Secure the ziplock in place on the drive axle with a couple of drops of superglue.
15. Tie one end of the string to the loop at the end of the lever arm.
16. Make a loop in the other end of the string.
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SCIENCE ACTIVITY 1: Simple Machines
Objective
Students identify the simple machines used to create and power a mousetrap car.
Background Information
A machine is a device that makes work easier. Machines can make work easier by increasing
force, changing the direction of a force, or by changing the speed at which the force acts.
Simple machines are made up of one or two parts and are not powered by an electrical motor.
There are six types of simple machines:
1. pulley – define and add picture
2. wedge – define and add picture
3. inclined plane – define and add picture
4. wheel and axle – define and add picture
5. screw – define and add picture
6. lever – define and add picture
Time
45 minutes (will vary with group size)
Materials
 completed mousetrap car
 “Simple Machines” information
 timer or stopwatch
 pencil
Vocabulary
 spring
 machine
Procedure
1. Using a timer or a stopwatch to keep track of time, find as many examples of simple
machines in your mousetrap car as possible in one minute.
2. Write down each type of simple machine you can identify.
3. Justify your examples. Write a brief statement explaining why you think each example
represents that type of simple machine.
Discussion
You may want to let students discuss whether or not they think a spring is or is not a simple
machine. Ask students who think it is a simple machine to classify it as one of the six types of
simple machines. Ask students to think about what the spring is doing in the mousetrap and in
the car. The spring is actually storing and converting energy. It is not a simple machine.
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SCIENCE ACTIVITY 2: Calculating Velocity
Objective
Students calculate the velocity of a mousetrap car.
Time
45-90 minutes (will vary with group size)
Materials
 completed mousetrap car
 graphite (optional)
 tape measure
 masking tape
 stopwatch
 “Velocity Data Sheet” (next page)
 pencil
Vocabulary
 velocity
 variation
Procedure
1. Locate a smooth, flat surface – preferably a hallway or classroom floor space – on
which to set up a testing track.
2. Using the masking tape, create a starting line. To do this, place a piece of masking tape
approximately 2 feet long on the floor. This should give you enough space to place two
cars on the starting line at one time.
3. Measure a distance of 10 feet from the starting line and place another 2 feet long piece
of masking tape on the floor. This is the finish line.
4. Place your car on the starting line. The person serving as the timer should give the
signal to release your car. Record the time for Test Run 1 on the data sheet.
5. Complete as many tests as time allows.
6. Explain any significant variations in time from one test to another. For example, if the
time for Test Run 1 was 15 seconds and the time for Test Run 2 was 30 seconds, you
may want to include a brief note about why you think this occurred. It could be
something as simple as a wobbly wheel or a change in the angle of the lever arm.
However, it will be important when you analyze the data later that you have as much
information as possible.
7. Calculate velocity of the mousetrap car for each run. Calculate the average velocity of
the vehicle. Record these values on the data sheet.
8. Complete the data sheet.
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VELOCITY DATA SHEET
Test Run
Times (s)
Distance (ft)
1
2
3
Velocity (ft/s)
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10
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To calculate the car’s average velocity, add the velocities for each run and divide by the total
number of test runs completed.
Average Velocity = _________________ ft/s
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SCIENCE ACTIVITY 3: Relating Circumference and Distance
Objective
Students calculate the circumference of the mousetrap car’s wheels and use that value to
determine the linear distance traveled.
Time
90-180 minutes (will vary with group size)
Materials
 completed mousetrap car
 ruler
 “Circumference Data Sheet (next page)
 calculator
 pencil
Vocabulary
 diameter
 radius
 circumference
 revolution
Procedure
1. Using the ruler, measure the diameter and radius of one of the mousetrap car’s wheels.
Record these values on the data sheet.
2. Calculate the circumference of the wheel.
3. If the wheel makes one complete revolution, determine how far the wheel will travel.
4. Using what you’ve learned about the circumference of the wheel and its relationship to
the distance traveled by the wheel with each revolution, complete the data sheet.
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VELOCITY DATA SHEET
Radius (cm)
Distance
Diameter (cm)
Circumference C = pi xd
Circumference (cm)
Number of Revolutions
Rev = d/C
Note: use the fact that 1 inch = 2.54 centimeters to complete this data sheet.
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SCIENCE ACTIVITY 4: Vehicle Mass and Distance Relationship
Objective
Students find the effect of a car’s mass on the distance traveled.
Time
90-180 minutes (will vary with group size)
Materials
 completed mousetrap car
 graphite (optional)
 tape measure
 masking tape timber cutter or X-ACTO knife
 dremel tool or portable hand drill
 wire cutters
 needle-nose pliers
 cool-met glue gun and glue slugs
 washers
 scale or balance for finding the mass of cars
 “Vehicle Mass and Distance”
 pencil
Vocabulary
 weight
 mass
 protocol
 variable
 hypothesis
 guess
Procedure
1. Locate a smooth, flat surface – preferably a hallway or classroom floor space – on which to
set up a testing track.
2. Using the masking tape, create a starting line. To do this, place a piece of masking tape
approximately 2 feet long on the floor. This should give you enough space to place two cars
on the starting line at one time.
3. Find the mass of the mousetrap car. Record the stock car’s mass on the data sheet.
4. Place the stock mousetrap car on the starting line.
5. Release the car and measure the total distance traveled by the car. Establish a protocol for
measuring the distance. Will you measure from the starting line to the rear of the car or
from the starting line to the front of the car?
6. Record the distance measurement on your data sheet.
7. How do you think weight will affect the mousetrap car?
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8. Record a hypothesis on your data sheet.
9. Add washers or laboratory masses to the car and complete Steps 3-6 again. You will need
to complete at least three tests of the car at different masses. For each test, record on your
data sheet the car’s weight and the distance traveled.
10. Use the data from your tests to create a graph that shows any relationship between mass
and distance.
11. Compare your data with that of other students. Record your recommendations for building a
car that will go the maximum distance.
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Engineering Challenges I
Objective
Students design a mousetrap car to reach the maximum distance possible.
Engineering Challenges II
Objective
Students design a mousetrap car that will travel to an exact distance.
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