From cars and trucks to planes and trains, brakes work in a similar way on most different vehicles. There are even brakes in wind turbines! Here's a quick comparison of some common brake systems.
Bicycle
If you ride a bicycle, you know all about brakes. If you want to stop suddenly, you squeeze the brake levers on the handlebars. Thin metal cables running to the back and front wheels pull on small calipers, forcing thick rubber blocks to press against the wheels. As they do so, friction between the blocks and the metal wheel rims generates heat, reducing your kinetic energy, and bringing you safely to a stop.
Although most bicycles still use caliper brakes, some use disc or drum brakes instead (described below).
Motorcycle
Motorcycles typically have disc brakes comprising a rotor and a brake pad. The rotor is a disc with holes (or slots) in it mounted on the side of the wheel. A brake pad, operated by a hydraulic cable, jams against the rotor to slow it down by friction. The holes in the rotor help to dissipate the heat generated.
Steam locomotive
The brakes on a steam locomotive work the same way as a car's and are even more obvious. You can see the brake just behind the wheel in this photo. It clamps against the locomotive's driving wheels to slow them down. Since there are no tires on the wheels, the friction that stops the train comes from the immense weight of the locomotive pressing the metal wheels down onto the track.
Airplane
Airplanes have brakes inside their wheels to help bring them to a stop on the runway, but they can also use air brakes to increase drag (air resistance) and slow themselves down—a bit like parachutes. Jet fighters often have a speed brake, which is a large metal plate just behind the cockpit that can be hydraulically raised to increase drag and braking.
Wind turbine
Wind turbines have brakes to stop their rotors (propellers) turning too quickly. The brake is mounted inside the nacelle (the square-shaped casing behind the propeller that contains the gearbox and generator). Most turbines have an anemometer on them to measure the wind-speed. If it rises above a safe level, the brakes come on automatically and bring the rotors to a standstill. It's a shame, because higher wind speeds mean more energy could be produced. But safety always comes first!
A closer look at car brakes
Most cars have two or three different types of braking systems.
Disc brakes
Peer through the hubcap of a car's front wheels and you can usually see a shiny metal disc just inside. This is called a disc brake. When the driver steps on the brake pedal, a pad of hard-wearing material clamps onto the brake disc and rubs it to make it slow down—in a similar way to bicycle brakes.
Drum brakes
Some cars have disc brakes on all four wheels, but many have drum brakes on the back wheels, which work in a slightly different way. Instead of the disc and brake block, they have shoes inside the hollow wheel hub that press outwards. As the shoes push into the wheel, friction slows you down.
Handbrake
A car's handbrake applies the two rear brakes (disc or drum) in a slower, less forceful way through a lever that's typically located between the front seats. When you pull on the brake, a system of levers tugs on a pair of sturdy cables that apply the brakes to the back wheels. The handbrake system is completely mechanical and, unlike the conventional pedal brakes, doesn't use hydraulic fluid. That means it can be used (with very great care!) as an emergency braking system if the normal brakes fail.
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