Mousetrap Cars
When you build a mousetrap car designed for distance, there are many things to consider:
• The size of the wheels
• The size of the axle
• The length of the arm
• The length of the car
• Torque
• The mass of the car
• Inertia
• Friction
All of these factors affect the distance that a mousetrap car can travel.
         The ratio of the size of wheel to the axle both affects the pulling force (torque) and the pulling distance.  A greater ratio (larger wheels, smaller axle) will give it more distance but less power.  If it has too little power, it will not move at all because the mousetrap is not powerful enough to pull it.
         The length of the lever arm also affects the distance and torque.  A longer arm gives greater distance, but less torque.  IMPORTANT FACT:  Increasing the lever arm beyond the axle does NOT increase the pulling distance, it only increases the mass.  It should not be longer than the car.  To effectively increase the length of the lever arm you must place the mousetrap farther away from the axle by placing it at the front of the car and possibly lengthening the car.
         The mass of the car should be as small as possible.  Mass is what causes inertia. A car with less inertia requires less torque to move, and therefore can have a greater pulling distance.  Rotational inertia is the inertia of the wheels; it also makes it harder for the car to move.  To decrease rotational inertia, you can try removing the weight from the wheels.

Good materials to use

For the back wheels you should use CDs or records.  To get these to fit on the axle, you need ¼ L rubber sink washers and Epoxy glue.  The washers can be found at Home Depot or Lowe’s.  Epoxy is a type of glue that is very strong and can also be found at home improvement stores.  For a CD, you put the sink washer in the center hole (it should fit almost tightly), and then put Epoxy around it.  Be careful not to get any in the hole in the sink washer.

For the front wheels, you should use either CDs or something smaller.

For the axle, you should use a small metal pole that fits in the ¼ L rubber sink washers.  Use metal eyehooks that screw into the base of the car to keep the axle in place.

For the base of the car, you should use balsa wood to reduce the mass.  You should be careful though because balsa wood is very light and breaks easily.
Mousetrap car links
A good mousetrap car site