FRICTION

introductions

friction

An interesting thing about friction is that it usually takes more force to break an object loose than to keep it sliding. There is a coefficient of static friction, where the two surfaces in contact are not sliding relative to each other. If the two surfaces are sliding relative to each other, the amount of force is determined by the coefficient of dynamic friction, which is usually less than the coefficient of static friction.

For a car tire, the coefficient of dynamic friction is much less than the coefficient of static friction. The car tire provides the greatest traction when the contact patch is not sliding relative to the road. When it is sliding (like during a skid or a burnout), traction is greatly reduced.

In general, there are two categories of brakes, the Disc Brakes and the Drum Brakes. Many modern cars have disc brakes on the front wheels and drum brakes on the rear wheels. More expensive models may have disc brakes on all four wheels. Only very old or very small cars tend to have drum brakes on all four wheels.

By the development of car technology, the hybrid and electric car, the regenerative brake system is applied. Regenerative braking recovers the kinetic energy during braking. When the driver step on the brake, the electric motor switch to generator mode. It converts a portion of kinetic energy into electrical energy and stored in high-voltage battery.

Disc Brakes consist of a brake disc, a brake caliper and a pair of brake pad. When the brake pedal is pressed, the hydraulic fluid causes the brake caliper to press the brake pad against the brake disc. The rubbing of the brake pad against the brake disc generates friction, which converts kinetic energy into heat in the brake pad.

Derived technology of disc brakes is Magneto-rheological Brakes, named MRF Brakes. It utilizes magneto-rheological fluid (MR fluid) as the friction media instead a conventional brake pad. The discharge of electric current to the MR fluid will create magnetic field which generate friction to the rotating disc. The braking action is occurring.

We live in the world where motion is always being a part of it. In term of motion, brake has the important role to play.