- 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.
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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,
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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)