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Mouse Trap Vehicle: Finding Wheel Traction

March 07, 2012

Earth shattering secrets for building record setting and winning mousetrap cars and racers. Here you will find all the latest and greatest untold construction secrets so you can build your very own mousetrap vehicle.


To find the amount of grip or traction a drive wheel has on the floor.

Equipment Needed

  • Spring scale or force probe
  • String
  • Tape to lock wheels


Grip or traction is what prevents the wheels of a mousetrap car from spinning out at the start. The amount of grip is also what determines the acceleration of your vehicle. The more grip or the more traction your vehicle's wheels have on the floor surface the greater the acceleration that is possible. If you are making a speed-trap or a power pulling vehicle you want to test different materials on your wheels to make sure you have the maximum traction possible; for example, rubber balloons on wheels, rubber bands on wheels, different compounds, etc. Once you have found the maximum traction, you can adjust the length of your mouse trap's lever arm in order to achieve the greatest possible pulling force. Shorter lever arms have greater force for more power or acceleration for your vehicle. keep in mind that the amount of traction will vary from surface to surface because not all surfaces have the same grip. Example, your car will have more grip on concrete than on ice; because of this, you must test your mousetrap vehicle's traction on the actual course where you will be running your contest or activity. In this activity you will find that actual for of traction and the coefficient of friction between your vehicles drive wheels and the floor. The coefficient of friction tells you how slippery two surfaces are together. The larger the coefficient of friction, the more grip or traction your vehicle will have with that surface.

ƒ = μN

formula 1: The force of friction [ƒ] depends on how slippery two surfaces are together called the coefficient of friction [μ] and how hard the surfaces are pressed together [N]. The coefficient is measured in newtons, the normal force in newtons, and the coefficient is newtons over newtons.

N = mg

formula 2: The normal force (N) is how hard two surfaces are pressed together or the weight of the object. This means that the normal force (N) is equal to the weight of the car or the mass (m) of the car times the acceleration of gravity (g).

Step 1:

Use a piece of tape or anything else that might work to lock the drive wheel(s) and prevent them from turning. The non-drive wheels should be aloud to turn freely.

lock the drive wheels: use a piece of tape or anything else to temporarily prevent the drive wheels from turning.

Step 2:

Attach a sensitive spring scale or force probe to the front of the car. It is best to tie a string to the front of that car and then attach the spring scale to the string.

the set-up: Attach a sensitive spring scale or force probe to the front of the car with a string.

Step 3:

Pull the vehicle on the race surface at an even force and constant speed keeping the scale or force probe parallel to the road. Pull the vehicle several time and record the readings each time calculating an average. The force required to drag your car is equal to the force of traction, calculate the average and record.

force of traction = _____ N

measure the traction: Pull the vehicle at a contact speed making sure to keep the string parallel to the floor

Step 4:

The normal force is the amount of weight supported by the drive wheels and is not the full weight of the vehicle. The normal force for the drive system is the proportion of the vehicle's weight supported by the drive axle. Lift the drive axle as pictured with the force probe until the drive wheels just lift off the floor. Record this number as the force on the drive wheels.

normal force = _____ N

measure the normal force: Lift the drive axle as pictured with the force probe until the drive wheels just lift off the floor.

Step 4:

Using the formula, divide the force of traction by the force on the drive wheels

μ = f / N

coefficient of friction = _____ N/N

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