Death-defying designs for car safety

Glossary

coefficient of friction. The ratio of the force that is necessary to move an object and the weight of the object. It is a measure of the amount of friction that exists between two materials as one slides over the other. The coefficient of friction is zero if there is no friction, and it is infinite if no motion is possible. For more information see How Brakes Work: Friction (How Stuff Works, USA).

kinetic energy. Kinetic energy is the energy associated with a moving object (energy of motion). For more information see Energy basics (Box 3 of Nova: Science in the news topic, Wind power gathers speed).

traction. The amount of forward thrust that a wheel can provide before it slips. It is the product of the weight bearing down on the wheel (generally 25 per cent of the vehicle weight on a level road) and the coefficient of friction, which depends on the nature of the tyre and the surface of the road. Traction helps determine the steepest road a vehicle can climb.

weight. The downward force of gravity on an object.

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Page updated December 2003.