THE MOUSETRAP CAR SCIENCE ACTIVITIES Page What Is A Mousetrap Car and How Does It Work? 2 Builder s Tips 2 SCIENCE ACTIVITY 1: Simple Machines 3 SCIENCE ACTIVITY 2: Calculating Velocity 4 SCIENCE ACTIVITY 3: Relating Circumference and Distance 7 SCIENCE ACTIVITY 4: Vehicle Mass and Distance Relationship 9 Engineering Challenges I & II 11 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. 2
Builder s Tips 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. 3
SCIENCE ACTIVITY 1: Simple Machines 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. 4
SCIENCE ACTIVITY 2: Calculating Velocity 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. 5
VELOCITY DATA SHEET Test Run Times (s) Distance (ft) Velocity (ft/s) 1 10 2 10 3 10 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 6
SCIENCE ACTIVITY 3: Relating Circumference and Distance 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. 7
VELOCITY DATA SHEET Radius (cm) Diameter (cm) Circumference C = pi xd Distance Circumference (cm) Number of Revolutions Rev = d/c Note: use the fact that 1 inch = 2.54 centimeters to complete this data sheet. 8
SCIENCE ACTIVITY 4: Vehicle Mass and Distance Relationship 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? 8. Record a hypothesis on your data sheet. 9
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. 10
Engineering Challenges I Students design a mousetrap car to reach the maximum distance possible. Engineering Challenges II Students design a mousetrap car that will travel to an exact distance. 11