A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction. 制动器是一种通过吸收运动系统的能量来抑制运动的机械装置。它用于减慢或停止移动的车辆、车轮、车轴，或防止其移动，通常通过摩擦实现。

Most brakes commonly use friction between two surfaces pressed together to convert the kinetic energy of the moving object into heat, though other methods of energy conversion may be employed. For example, regenerative braking converts much of the energy to electrical energy, which may be stored for later use. Other methods convert kinetic energy into potential energy in such stored forms as pressurized air or pressurized oil. Eddy current brakes use magnetic fields to convert kinetic energy into electric current in the brake disc, fin, or rail, which is converted into heat. Still other braking methods even transform kinetic energy into different forms, for example by transferring the energy to a rotating flywheel. 大多数制动器通常使用两个压在一起的表面之间的摩擦力将移动物体的动能转化为热量，但也可以使用其他能量转换方法。例如，再生制动将大部分能量转换为电能，电能可以储存起来供以后使用。其他方法将动能转化为储存形式的势能，如压缩空气或压缩油。涡流制动器利用磁场将制动盘、翅片或导轨中的动能转化为电流，并将其转化为热量。还有一些制动方法甚至将动能转化为不同的形式，例如将能量转移到旋转的飞轮上。

Brakes are generally applied to rotating axles or wheels, but may also take other forms such as the surface of a moving fluid (flaps deployed into water or air). Some vehicles use a combination of braking mechanisms, such as drag racing cars with both wheel brakes and a parachute, or airplanes with both wheel brakes and drag flaps raised into the air during landing.

Since kinetic energy increases quadratically with velocity, an object moving at 10 m/s has 100 times as much energy as one of the same mass moving at 1 m/s, and consequently the theoretical braking distance, when braking at the traction limit, is 100 times as long. In practice, fast vehicles usually have significant air drag, and energy lost to air drag rises quickly with speed.

Almost all wheeled vehicles have a brake of some sort. Even baggage carts and shopping carts may have them for use on a moving ramp. Most fixed-wing aircraft are fitted with wheel brakes on the undercarriage. Some aircraft also feature air brakes designed to reduce their speed in flight.

Friction brakes on automobiles store braking heat in the drum brake or disc brake while braking then conduct it to the air gradually. When traveling downhill some vehicles can use their engines to brake.

When the brake pedal of a modern vehicle with hydraulic brakes is pushed against the master cylinder, ultimately a piston pushes the brake pad against the brake disc which slows the wheel down. On the brake drum it is similar as the cylinder pushes the brake shoes against the drum which also slows the wheel down.

Single pivot side-pull bicycle caliper brake; Disc brake on a motorcycle; Rendering of a drum brake

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 六级/考研单词: brake, inhibit, seldom, accomplish, friction, convert, rotate, fluid, flap, deploy, parachute, velocity, luggage, cart, automobile, conduct, gradual, pedal, cylinder, pad, render