BRAKES: How They Work | Science Garage
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BRAKES: How They Work | Science Garage

– We’ve all been there. You’re driving along
when something happened. (crashes) Today, we’re gonna look at the main thing that saves your butt in
situations like that, your brakes. Alright, everybody bring it in. – [All] And brakes! – The core concept of a vehicle’s
braking system is simple. An object is in motion and it needs to stop being in motion. Brakes use friction to decelerate. The wheel has energy in
the form of movement. The brakes apply friction and create heat energy. Once all the movement energy
is transformed into heat, your car stops. It’s not magic, it’s physics. To stop, you need friction. This simple concept is what almost all vehicle share in their efforts to come to a stop. What isn’t shared between vehicles is how that friction is applied after the pedal is pressed. The very first brakes were just pieces of wood
that pushed on the wheels. It worked, but it wasn’t that great because it beat the crap out of the wheel. (speaks in Russian) The simple solution was to attach something to the wheel and slow that down. In 1900, Wilhelm Maybach became the first car maker to put a drum on a wheel
to assist with braking. Slowing down the drum meant the
wheel woudn’t take the wear. Good thinking, guys. Here’s what a drum brake looks like. This drum is attached to the wheel. Inside of it are these
two heat-resistant pads. When you press the brake pedal, these pads are squeezes
up against the drum. The pad slow the drum and the drum stops the wheel. Early cars also used a
bunch of cables and pulleys to get the pressure from
the pedal to the wheel. When you push the pedal,
it pulled the cable, and the brake wires needed
a lot of maintenance, and often they snap when
you needed them the most. Another downside was
the precision required. If a lever was off or a
wire was tensioned wrong, the different wheels would receive different braking pressures, and that’s just unsafe. Hydraulic brakes on the other hand use pressurized fluid to push the brakes. When you hit the pedal, a plunger depresses in
the master cylinder. That sends the pressure
through all of the brake lines to all four wheels at once. Hydraulic brake lines rarely rupture. They don’t require the
maintenance of mechanical lines and they required very little
pressure from the pedal to be effective. By 1950, hydraulic brakes were really the only braking
systems left in cars. Drum brakes were pretty good, and we use them in most
of the production cars up into the ’80s. Their major drawback, however, was that under intense
conditions with frequent braking, they got really hot. If they’re too hot, they can’t change the energy of motion into heat. That’s bad, because that’s when
you need them the most. Let’s build some better brakes. An increased coefficient
means better braking, but it also means you need better cooling. One way to create more friction is with the materials in the pad. Pads have to be strong
enough to stop a wheel, but strong enough not to damage the drum or sound like death. (laughs) Another way to increase friction
is to apply more pressure. Drum brakes push out. The brain trust making brakes realized you can create more
pressure by squeezing in. And lastly, you have to
increase suffice area the greater surface
area means more friction The best way to improve
friction and avoid heat is lose the drum, squeeze to a stop, and increase surface area. So instead of a drum, they use a disk. The disk or rotor is attached to the wheel and rides inside a caliper. The caliper squeezes the
brake pads against the rotor and the wheel comes to a stop. Disk brakes cool off better because they’re not inside of a drum. The air cools them. The bigger the brake and
caliper combination is, the more friction they can generate and the more easily they
can dissipate the heat. Like many automotive advancements, the first disk brakes used in racing were in Formula 1 in 1951. In 1955, Citroen became the first company to put them on production cars. They were more expensive to manufacture, but as cars became faster, disk brakes became necessary. That’s not to say that drum
brakes are more dangerous. We still use drum brakes. When a vehicle slows, it’s weight gets transferred mostly to the front axle. The front brake usually
does about 70% of the work, leaving the back brakes
with a lighter load. James, what are you doing, man? – What are you doing driving
in the freaking street? – Sorry almost hit you. We cool? (munching) – Because drum brakes are cheaper and simpler to produce and maintain, most auto makers use them on lighter cars or entry level models because, well, because they’re adequate. The rotors can have any number of tweaks to make them more effective, and most of them have to do with getting rid of that heat energy. Some have a gap in the
middle to let air in. Some have fins in this gap to pull air in, and some would have holes all around so that they could let air in and out all over the place. Your car’s brakes probably won’t get above 400 degrees, which is still super hot. That would cook a pizza in 50 seconds. – Pizza? – Most pads are made of
semi-metallic material, synthetics mixed with
difference proportions of flaked metals. Race disk brakes can reach
temps over 1,000 degrees. (whirring) So race pads are composed
of sintered steel without any synthetic additives. They work best at high temperature because the demand on them is so high. If you put them on your daily, they’re gonna squeal like heck. Just ask Tony. It’s adorable, right? He’s got his headphones on. If your brakes squeal, that usually means your almost out of pad. Manufacturers put an indicator in them. So they shriek like banshee. (shrieking) Even if it turns out that
that’s not the issue, squealing brakes mean
something is not right. They could be vibrating
and not lined up right, or maybe some foreign matter got in there. And that can cause pretty
big damage in the long run. Ever since we started going fast, we had to look for better ways to stop. We’ve come a long way from just smashing wood on wheels. So appreciate your brakes because they keep you from being dead. Okay, I guess it’s time to put a stop to this episode of Science Garage. No one wrote that. Thanks to Skillshare for
sponsoring this episode. Look, if you’re watching Science
Garage, you like learning. And if you like learning,
you’ll love Skillshare. Skillshare is an online learning community with thousands of classes in design, business, technology, and more. You wanna make cool motion
graphics of a brake drum? Well, they got courses for that. You wanna make sick beats
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pump half cup mocha lattes. And what’s even better is that the first 1,000 people to sign up with the link in the description will get their first
two months for 99 cents. So go to or click on the link in the description. Go get skilled, get Skillshare. Guys, thanks for talking with me today about how brakes work. If you guys wanna know some of the best modification
you can do your own car, check out this vid from Tony. If you guys wanna know
other stuff about safety, check out this video about helmets. Guys just another reminder, we’ve got merchandise. Do you guys like this shirt
or you want a sticker? Go to We do a lot of fun stuff. If you wanna see more of it, guys, follow us on Instagram @donutmedia. You follow me at Instagram @bidsbarto. I love reading your comments. I love talking to you guys. Thanks for watching. Don’t tell my wife I took her brakes. It’ll be on tomorrow. (clink) (cheerful music)

100 thoughts on “BRAKES: How They Work | Science Garage

  1. Seeing as I am able to completly lock up my breaks when I slam on the pedal, what is the benefit of upgrading the breaks? It seems like it's pointless, seeing as my breaks can break harder than my tires can grip… What am i missing?

  2. Wait didn't anybody notice he says only the wheels have "kenetic engery" as he calls it. The whole car or truck is moving so when you brake it's not just turning the kinetic energy of the moving wheels into heat which is just a small part of fhe total kinetic of the car, it's turning the kinetic energy of the total mass of the car into heat. And right after he makes this mistake he proudly says "It's not magic, it's physics!" :

  3. I came here to find out why/how hydraulic brakes require a running engine and pullies.. not sure I saw that anywhere. Also is there such a thing as Electric brakes? Wondering about EV conversions and Braking systems.

  4. The basic theory of friction is force x coefficient of friction = friction force
    No where in there is area.
    Explain yourself B A R T

  5. an object is moving, it need's to stop moving ya'll still using brakes? Why don't you just stop moving? #madlad

  6. 3:17 "A greater surface area means more friction." That's actually not exactly true. Friction depends only on the normal force and the friction coefficient between the two materials, that's it; perhaps he meant to say that increasing the surface area can increase the normal force which would thereby increase the friction.

  7. Kinetic energy? Is that how it's spelt in the US or something? Don't know if I should trust these vids anymore

  8. If front wheel brake do 70%job done than why does bigger vehicles like trucks and dumpers have small brake drums,pads,piston etc infront wheels and bigger in the rear wheel

  9. What about regenerative braking, converts back to electrical energy? Oh wait thats electric trains sorry…..

  10. One important thing you missed is that stopping distance is effected by breaks, tires and weight

  11. 5:20 how does 400° cook a pizza in 50 seconds when my oven takes 12-18 minutes?! Should I be making my pizza on my rotors?!

  12. I was waiting to learn how brakes work. I guess I'll wait for another episode with that info. Until then, wish me luck!!

  13. Hey Science Garage, can you explain how regenerative brakes work? I have a BMW 328i and the manual says braking for longer is better than shorter distances, for energy recuperation. Also, it'd be nice to know why an engine at standby at a stoplight is better economy savings. Heck why don't you do a science garage on Hybrid Car's energy efficient qualities and characteristics!

  14. What the fuk? At first i thought “alright guys got it’s a bit much” now i cant get enough. I saw car with a donut sticker. 😃😃

  15. Rookie question. On disc brakes I understand how everything works with the floating caliper applying even pressure through hydraulics to both sides of the disc. My question is what causes the pads to retract? I see guys replacing pads and squeezing them right up to the disc. I know the piston applies the pressure for squeezing but what backs them off? I know they are extremely close to the rotor when no pressure is being applied so I'm guessing that the when the floating caliper with the spring loaded pins backs off the pressure, it just leaves the pads riding extremely close to the rotor if not barely touching which is why you almost always hear contact on any vehicle (motorcycle etc.) when just spin the wheel or roll it, like on my motorcycle. Thanks in advance for anyone's help.

  16. Just a quick correction increasing the surface area does not increasing your breaking power. The equation for a friction force is F=μN (friction force=coefficient of friction*normal force). Normal force would be how hard your squeezing the diskbreak, coefficient of friction is how much friction the two materials have when rubbing together, which when multiplied together gives you your total friction force. Surface area does not matter because as you increase it your N is spread out over that area giving you less friction per square inch. The larger surface area helps because there is more area to disperse the heat, not because it gives you more friction.

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