Speaker 1: Get in touch with technology with tech Stuff from how
Speaker 1: stuff works dot com. Hey there, and welcome to tech Stuff.
Speaker 1: I'm your host, Jonathan Strickland. I'm an executive producer with
Speaker 1: How Stuff Works, and I heart radio and I love
Speaker 1: all things tech. And you know, we've been going pretty
Speaker 1: fast with tech stuff over the past I don't know, decade,
Speaker 1: So I felt maybe it was time to apply the
Speaker 1: brakes a little bit. I don't mean to slow down
Speaker 1: the show or stop it, but rather to take time
Speaker 1: to talk about how breaks work and the science surrounding breaks,
Speaker 1: because puns are sort of a thing I do, but seriously,
Speaker 1: I thought this would give us a chance to talk
Speaker 1: about mechanical and hydraulic systems as well as the science
Speaker 1: that's behind breaking, the physics that are involved. So first,
Speaker 1: let's talk about what makes breaks no necessary in the
Speaker 1: first place, which is pretty obvious stuff, but it leads
Speaker 1: into a discussion about physical forces that guided the whole
Speaker 1: evolution of breaks. So, a body in motion has momentum.
Speaker 1: Momentum is a quantity of movement. It depends upon two things,
Speaker 1: the mass of the object that's in motion and how
Speaker 1: quickly that mass is moving. So really comes down to
Speaker 1: how much of the stuff is there and how fast
Speaker 1: is it going. A simple equation would be momentum equals
Speaker 1: mass times velocity. So if you have something with a
Speaker 1: low mass, like a bullet, but it's traveling at a
Speaker 1: high velocity, it has a pretty good amount of momentum.
Speaker 1: If you have something that's really really huge, like a glacier,
Speaker 1: but it's moving incredibly slowly, it still has a lot
Speaker 1: of momentum, because momentum depends upon both the mass and
Speaker 1: the velocity, not just one or the other. Now, if
Speaker 1: you have something that's of a pretty decent size, like
Speaker 1: a vehicle, and it's moving at a pretty good speed,
Speaker 1: then that has got a lot of momentum too. And
Speaker 1: that's a problem, right If you've got a mass that's
Speaker 1: moving at a pretty good speed and you need to
Speaker 1: stop that mass, you have to figure out how do
Speaker 1: you offset that momentum, How do you convert this movement
Speaker 1: energy into something else. So momentum is also a vector
Speaker 1: quantity vectors and physics have not just a magnitude but
Speaker 1: also a direction. Acceleration is the same. It has a
Speaker 1: magnitude and a direction. So to fully describe momentum, we
Speaker 1: need not just how many kilograms of mass are traveling
Speaker 1: at a speed typically in meters per second, but also
Speaker 1: the direction of travel. Now, a body and motion has
Speaker 1: kinetic energy as well. So to reduce momentum and stop
Speaker 1: a body in motion, you need to convert that kinetic energy,
Speaker 1: that energy of movement in to something else. Because we
Speaker 1: have to remember the laws of conservation, the laws of
Speaker 1: the universe. We we energy cannot be created, it cannot
Speaker 1: be destroyed. We cannot just make energy, we cannot destroy energy.
Speaker 1: We can convert it from one form into another. So
Speaker 1: breaks do this by converting the kinetic energy of an
Speaker 1: object in motion into heat through friction. And you've probably
Speaker 1: heard the term waste heat. Now what we mean by
Speaker 1: that is that we've got some sort of system. It
Speaker 1: can be pretty much any given mechanical system in particular,
Speaker 1: but really other systems as well, biological systems. Uh So,
Speaker 1: it could be pretty much anything. And in this system,
Speaker 1: some of the energy that we're depending on is going
Speaker 1: not to whatever it is we're trying to do, but
Speaker 1: rather into generating heat. So with a bicycle, some of
Speaker 1: the energy we're putting forth by peddling is not going
Speaker 1: directly to making us move we're losing it in the
Speaker 1: form of friction, and thus heat um really the heat
Speaker 1: that's generated from friction. That's the best way of putting it.
Speaker 1: The heat represents energy that we could not otherwise exploit
Speaker 1: for whatever it is we're trying to do. So here's
Speaker 1: another example, with an electrical generator. We might say that
Speaker 1: the friction of the moving parts inside that electrical generator
Speaker 1: means that some of the kinetic energy we would otherwise
Speaker 1: use to create more electricity is instead converting to heat,
Speaker 1: and that heat isn't being captured in any meaningful way.
Speaker 1: So the work we did two direct this kinetic energy
Speaker 1: to the generator was wasted. Some of that work we
Speaker 1: weren't able to get efficiency. So no system is perfect.
Speaker 1: Any system with moving parts is going to have friction
Speaker 1: to deal with. And there are a lot of super
Speaker 1: smart materials scientists out there who have worked really hard
Speaker 1: to develop stuff that generates very little friction, and that
Speaker 1: is in an effort to increase efficiency and minim eyes
Speaker 1: waist heat. But when it comes to breaks, we want
Speaker 1: that friction. That's what is stopping an object. So we
Speaker 1: need something that is really good at creating this friction.
Speaker 1: We want to convert that kinetic energy into heat and
Speaker 1: thus decrease the momentum of a fast moving massive object,
Speaker 1: perhaps even bringing that object to a complete stop, not
Speaker 1: just slowing it down, but stopping it. So in the
Speaker 1: very early days of break systems, even before there were cars,
Speaker 1: you were looking at a pretty simple device. And this
Speaker 1: would be in the horse drawn carriage era. You've got
Speaker 1: a carriage that's being pulled by horses. Even when the
Speaker 1: horses start to slow down, you know you still have
Speaker 1: the momentum of the actual carriage itself. You need to
Speaker 1: slow down the carriage uh to to come to a stop.
Speaker 1: So the break was typically a lever, and the long
Speaker 1: end of the lever was extended up towards the driver.
Speaker 1: That was the handle side, So the longside of the
Speaker 1: lever is the handle. On the short end of the
Speaker 1: ever was a wooden block. The wooden block was when
Speaker 1: you pull, the lever, would make contact, typically with the
Speaker 1: driver's side front wheel of the carriage to create that
Speaker 1: source of friction and convert the kinetic energy of the
Speaker 1: turning wheel into heat and thus slow and eventually stop
Speaker 1: the carriage. A lever is one of the classic simple
Speaker 1: machines it's a bar that rotates around the fulcrum, and
Speaker 1: a fulcrum is just a fixed point. So the length
Speaker 1: of the lever on either side of the fulcrum determines
Speaker 1: the amount of effort or force exerted or acquired per side.
Speaker 1: In a classic class one lever, lever makes certain types
Speaker 1: of work, such as lifting, easier by reducing the workload
Speaker 1: that is needed to affect a change to to create
Speaker 1: that lift. There are three classes of levers, and I
Speaker 1: just mentioned class one lever. That's the one where you've
Speaker 1: got a force that's applied on one end of the lever,
Speaker 1: you have a load the thing you're trying to move
Speaker 1: or activate on the other end of the lever, and
Speaker 1: the fulcrum is somewhere in between those two. If it's
Speaker 1: in the center of the bar, then the fulcrum ends
Speaker 1: up balancing loads on either side. If you put equal
Speaker 1: loads on either side, it should just balance out, kind
Speaker 1: of like you know, just a scale if you think
Speaker 1: of it that way. So a see saw or a
Speaker 1: teeter totter would be an example of a class one lever.
Speaker 1: If two people weigh the same on a seesaw, it
Speaker 1: balances out. But if you put a heavier person on
Speaker 1: one end and a lighter person on the other. The
Speaker 1: heavier person sinks down the lighter person goes up into
Speaker 1: the air. But if the heavier person were to scoot
Speaker 1: forward on the seesaw to decrease the space between the
Speaker 1: heavier person and the fulcrumb, then you would eventually balance out.
Speaker 1: And if the heavier person kept scooting forward to get
Speaker 1: closer to the fulcrum, the lighter person would eventually sink
Speaker 1: to the bottom and the heavier person would be up
Speaker 1: in the air. So by decreasing the disc dins between
Speaker 1: the load and the fulcrum, you can increase the the
Speaker 1: lifting power essentially, or the really you're decreasing the amount
Speaker 1: of force needed to lift that load, if you're really
Speaker 1: thinking about it that way, you're creating a mechanical advantage.
Speaker 1: But there are two other classes of levers. I should
Speaker 1: probably cover those because some of them actually factor into
Speaker 1: breaks as well later down the line. Class two levers
Speaker 1: put the fulcrum on one end of a bar, so
Speaker 1: instead of it being in the middle, somewhere the fulcrum
Speaker 1: the fixed point is actually on one end of the bar.
Speaker 1: The load is somewhere in the middle of the bar
Speaker 1: and the force is at the far into the bar.
Speaker 1: So a wheelbarrow is this type of lever, because these
Speaker 1: can be kind of difficult to imagine otherwise. But if
Speaker 1: you think about the wheel on a wheelbarrow is a fulcrum,
Speaker 1: and you put a load of stuff into the wheelbarrow itself,
Speaker 1: and then you lift the other side of the wheelbarrow
Speaker 1: by the handles. So the closer the load is to
Speaker 1: the fulcrum, the more the mechanical advantage you will have
Speaker 1: uh and the less you will the less effort you'll
Speaker 1: need to lift the handles for a given load. Or
Speaker 1: you can think of it another way, the heavier the
Speaker 1: load you will be able to manage as long as
Speaker 1: it's closer to the fulcrum. A class three lever has
Speaker 1: the fulcrum on one end, the load at the other end,
Speaker 1: and the lifting force is in the middle. Now, these
Speaker 1: leavers don't provide mechanical advantage, but they can increase the
Speaker 1: speed at which a force moves a load. A baseball
Speaker 1: bat would be an example of this, or even your
Speaker 1: your own forearm would be an example of this. But
Speaker 1: we're gonna leave the off from here because class three
Speaker 1: leavers don't really factor into the discussion for breaking, So
Speaker 1: the wooden block break is a Class one lever. On
Speaker 1: one end is the wooden block, its position near the
Speaker 1: carriage wheel. A little bit further up from the wooden
Speaker 1: block is the fulcrum, the fixed point closer to the
Speaker 1: wooden block than to the handle, and the other end
Speaker 1: of the lever, the long end has the handle, so
Speaker 1: the handle must travel a radar distance than the wooden block.
Speaker 1: When you pull back on the brake um, you are
Speaker 1: pulling the breakback much further than the wooden block has
Speaker 1: to travel to make contact with the the carriage wheel.
Speaker 1: But by increasing that distance, you reduce the amount of
Speaker 1: work you need to do on the force end to
Speaker 1: get a result on the load end. Uh. This is
Speaker 1: important because if you're going pretty fast and you need
Speaker 1: to slow down that wheel, you need to exert a
Speaker 1: good deal of force to create enough friction and convert
Speaker 1: that kinetic energy into heat. You couldn't easily do that
Speaker 1: if you were, let's say, just holding a wooden block
Speaker 1: and just trying to push the wooden block directly against
Speaker 1: the carriage wheel. You probably wouldn't be able to do
Speaker 1: that with enough force. To make a difference in a
Speaker 1: sufficient amount of time. By putting it on this lever,
Speaker 1: you can increase the amount of force you're exerting on
Speaker 1: the wheel itself on the carriage wheel through pressure with
Speaker 1: this wooden block, then you would if you were to
Speaker 1: do it directly. So the lever makes the job easier.
Speaker 1: Very important part of physics in general. The brake system
Speaker 1: made the transition from horse drawn carriages to some of
Speaker 1: the earliest automobiles in the nineteenth century, and it was
Speaker 1: the same sort of thing. They were using wooden blocks.
Speaker 1: The wheels on these early automobiles were often metal. There
Speaker 1: was no rubber tires yet, and they worked reasonably well
Speaker 1: under certain conditions, namely that the vehicles were traveling at
Speaker 1: slower speeds were talking below twenty miles per hour or
Speaker 1: below thirty two kilometers per hour, and traffic was pretty
Speaker 1: light in those days, so there weren't a lot of
Speaker 1: incidents where you would need to break quickly due to
Speaker 1: an increased amount of traffic on the streets. But you
Speaker 1: also weren't necessarily uh, it wasn't necessarily a good idea
Speaker 1: to go, like driving a car up a steep hill,
Speaker 1: for example, because your breaking system was pretty primitive. The
Speaker 1: only way you would prevent yourself from rolling backwards was
Speaker 1: either by applying more acceleration to overcome the force of
Speaker 1: gravity that's pulling you down, or to hold a break
Speaker 1: real strong against that wheel so that you're not slipping backward. Uh.
Speaker 1: This also was probably a good thing. Like that, It's
Speaker 1: probably a good thing you weren't going very fast, not
Speaker 1: just because the brakes were primitive, but because those wheels
Speaker 1: were metal. You would feel it when you would run
Speaker 1: over bumps in the road, of which there were many.
Speaker 1: It was very similar to if you remember my episodes
Speaker 1: about the history of the bicycle, the bone shaker, that
Speaker 1: it was a nickname for a type of early bicycle
Speaker 1: that was really uncomfortable to ride. It was a very uh,
Speaker 1: stiff ride, you might say. But it was clear the
Speaker 1: lever approach wasn't going to remain sufficient as cars were
Speaker 1: getting faster and heavier and traffic was increasing. You could
Speaker 1: stop a faster car with a lever breake, but it
Speaker 1: would take longer as you converted that kinetic energy into
Speaker 1: heat through friction, so you didn't come to a stop
Speaker 1: in as reasonable amount of space. You know, and an
Speaker 1: increase in traffic, you had a decreased the email of
Speaker 1: time you had in order to slow down to avoid collisions.
Speaker 1: So something had to change. A couple of people came
Speaker 1: up with some very clever alternatives. One was a proposal
Speaker 1: that was made. It was actually not just proposed, it
Speaker 1: was developed. It was the creation of Elmer Ambrose Sperry
Speaker 1: of Cleveland, Ohio. Sperry's solution involved using disc brakes. Now
Speaker 1: I'm going to cover modern disc brakes a little later
Speaker 1: in this episode, but it's good to just go ahead
Speaker 1: and then explain what the general idea was because it
Speaker 1: remained the same even later on. So let's say you've
Speaker 1: got a wheel, and you've got that hub of the wheel.
Speaker 1: This is part that turns on the axle. Attached to that,
Speaker 1: you have a disk that is really just part of
Speaker 1: the hub of the wheel, but it's separate from the tire.
Speaker 1: So you've got this free standing disc. Positioned over this
Speaker 1: disc is a set of calipers, so that either side
Speaker 1: of the caliper are on either side of the disk,
Speaker 1: and it can pinch down on the disk, just like
Speaker 1: your fingers would pinch down if you had let's say
Speaker 1: a spinning frisbee between two fingers and you rut uh.
Speaker 1: You know, your friend is holding their two fingers together,
Speaker 1: and the frisbee is spinning around on the axle of
Speaker 1: those two fingers. If you brought your fingers like calipers,
Speaker 1: right on the gadge and then pinched, you could stop
Speaker 1: the frisbee and its spin. That's the same idea as
Speaker 1: this set of disc brakes the the In a sense,
Speaker 1: it's working very similar to the way the wooden block
Speaker 1: that would press directly against the wheel itself works, except
Speaker 1: instead of of hitting the wheel, you're hitting this disc
Speaker 1: that's attached to the wheel. Um. Pretty clever. And Sperry
Speaker 1: was working on an early electric vehicle. You may remember
Speaker 1: in some of my previous episodes, I've talked about how
Speaker 1: electric cars actually pre date internal combustion engine cars. The
Speaker 1: earliest automobiles were electric vehicles, not not gasoline powered vehicles.
Speaker 1: So he's working on this electric car, and he was
Speaker 1: actually using electro magnetism to close those calipers, to shut them,
Speaker 1: to attract the pincher to the disk and have it
Speaker 1: clamped tight enough to start to break the wheel. Uh.
Speaker 1: Springs that were attached to the calipers would create the
Speaker 1: force that would allow the calipers to open up again
Speaker 1: once the electro magnetic field went away. So if you
Speaker 1: were to step on a brake in Sperry's design, you
Speaker 1: would cause a current to flow through the braking system,
Speaker 1: thus generating the electromagnetic field and forcing the calipers closed
Speaker 1: and breaking the disk, breaking b R A K I,
Speaker 1: n G. The disk. Letting the foot pedal brake would
Speaker 1: interrupt the current, so the field would dissipate, the springs
Speaker 1: on the caliper would pull the caliper open again. It
Speaker 1: was a very ingenious creation, but Sperry's invention didn't catch
Speaker 1: on in the States. A similar idea would take off
Speaker 1: in Europe, however, and I'll talk about a different breaking
Speaker 1: system that would see early success in the United States,
Speaker 1: and that early success would extend all the way into
Speaker 1: the modern day. But I'll do that in just a second. First,
Speaker 1: let's take a quick break. So right around the same
Speaker 1: time Sperry was working on the disc brake solution, Gottlieb
Speaker 1: Daimler was developing a different approach called the drum brake.
Speaker 1: Daimler's idea was to attach a drum mounted on an
Speaker 1: axle and to wrap a cable around that drum and
Speaker 1: pulling the brake would create tension on the cable, tightening
Speaker 1: it around the drum and creating the friction needed to
Speaker 1: slow and then stop a vehicle. So if you can
Speaker 1: think of maybe a spinning axle and then wrapping a
Speaker 1: belt around it and then pulling the belt, really taught
Speaker 1: so that that creates that friction and then slowing the
Speaker 1: axle down. It's similar to that. So you have this
Speaker 1: dedicated drum for this purpose. UH. This was an idea
Speaker 1: that will Helm Maybach used in nineteen o one in
Speaker 1: some early Mercedes designs, but it was Louis Renault who
Speaker 1: defined the drum break as a standard in vehicles. It
Speaker 1: was Renault's UH design that really took off. That being said,
Speaker 1: there are also a ton of different mechanics and engineers
Speaker 1: working on this problem, and so the idea may have
Speaker 1: been developing in parallel around the world. Renault gets the
Speaker 1: credit for making this the first really practical drum break,
Speaker 1: but lots of people were working on this because the
Speaker 1: automobile was a rising technology at the time. Now, the
Speaker 1: drum brake is a pretty clever invention, and a modernized
Speaker 1: version is still used in many vehicles today, though typically
Speaker 1: only for the rear wheels for most passenger vehicles. It
Speaker 1: was also the dominant form of breaking systems in the
Speaker 1: United States until the nineteen seventies, though in Europe things
Speaker 1: were a little different. The original drum brakes weren't great
Speaker 1: on flat surfaces. These drum brakes that had a a
Speaker 1: a belt or a strip of metal or something wrapped
Speaker 1: around a drum that would then tighten to slow things down,
Speaker 1: those worked fine on flat surfaces. A break race in
Speaker 1: nineteen o two pitted a horse drawn coach that had
Speaker 1: a lever style break against a Victoria horseless carriage that
Speaker 1: had an internal drum brake, and a custom vehicle that
Speaker 1: was created by a guy named Ransom E. Olds And
Speaker 1: he called it the Oldsmobile. Yep, that's where that comes from. So,
Speaker 1: like I said, the coach had a tire break, the
Speaker 1: horseless carriage had an internal drum break, which I'll talk
Speaker 1: about in a second, and the Oldsmobile had a different
Speaker 1: drum brake design that used a band of stainless steel
Speaker 1: wrapped around the drum. So pressing on the brake pedal
Speaker 1: rather than pulling a lever would contract this band. So
Speaker 1: that would grip the drum more tightly and thus create
Speaker 1: the friction. The oldsmobile proved it could stop in less
Speaker 1: time and thus travel the least distance while breaking than
Speaker 1: the other two vehicles. So this meant that for a while,
Speaker 1: external breaks, in which the breaking mechanism is on the
Speaker 1: outside of the drum, were more popular, but both external
Speaker 1: and internal drum breaking systems existed at the same time.
Speaker 1: So what was an internal drum break system. Well, in
Speaker 1: that case, you have the drum assembly that's mounted on
Speaker 1: a wheel or an axle, So just think of it's
Speaker 1: almost like a pot, right, It's just mounted on there
Speaker 1: and and everything is inside this pot. So you have
Speaker 1: these extendable parts inside the drum. They're called shoes. And
Speaker 1: these extendable shoes are anchored with respect to the car,
Speaker 1: so they are not rotating. They are stationary with respect
Speaker 1: to the chassis of the vehicle. So the drum rotates
Speaker 1: around these shoes as as the cars in motion. The
Speaker 1: shoes have breaking material, so a material meant to generate
Speaker 1: friction coding the surface of the shoe itself the stopping surface.
Speaker 1: So when you engage the brake, when you step on
Speaker 1: the brake, pedal A system extends these shoes on the
Speaker 1: inside of the drum, so that that breaking surface is
Speaker 1: rubbing up against the inside edge of that rotating drum.
Speaker 1: So it's the same effect that you were getting before,
Speaker 1: this idea of pressing a surface against a moving object
Speaker 1: in order to generate friction and convert kinetic energy into heat.
Speaker 1: It's just in this case it's happening on the inside
Speaker 1: of a rotating surface, not on the outside of the
Speaker 1: rotating surface. Uh. The this is really interesting stuff. It's
Speaker 1: a little difficult to envision just from my audio, I imagine,
Speaker 1: but if you really want to look into this and
Speaker 1: see some diagrams and some animations and things like that,
Speaker 1: How Stuff Works has several articles about breaks, including how
Speaker 1: drum brakes work, and that's incredibly useful. So if you
Speaker 1: want to check in on a visual aid, I highly
Speaker 1: recommend that I don't write for How Stuff Works anymore,
Speaker 1: but I still respect the heck out all the articles
Speaker 1: that are on that site. They are incredibly useful, especially
Speaker 1: for stuff like this, to get an understanding of these
Speaker 1: mechanical systems. So in addition, uh, these brakes would typically
Speaker 1: have some sort of cable or belt wrapped around the drum.
Speaker 1: So you would have a lot of cars that would
Speaker 1: have kind of a high red system where they have
Speaker 1: both external and internal breaking UH systems incorporated into the
Speaker 1: same overall brake system and create more friction more more efficiently,
Speaker 1: so that you could convert that kinetic energy into heat
Speaker 1: and stop faster. Now, early on, the external drum brake
Speaker 1: systems were believed to be superior. They could stop a
Speaker 1: car faster and less time less distance than internal ones,
Speaker 1: but they did have some big drawbacks. One of those
Speaker 1: was that the brakes would tend to unwind if you
Speaker 1: try to stop halfway up a hill. So you you're driving,
Speaker 1: you got a hill. Let's say you're in San Francisco.
Speaker 1: That's a great example. You're in San Francisco, you hit
Speaker 1: a hill, you're driving up the hill, and then you're
Speaker 1: coming up to an intersection where you have to stop. Well,
Speaker 1: that was an issue because the brakes would unwind. At
Speaker 1: that point. Gravity would create a backward pull on the
Speaker 1: car to pull it back down the hill, and that
Speaker 1: would cause the bands wrapped around the drum to unwind
Speaker 1: in the car would actually start to roll backwards. For
Speaker 1: that reason, early motorists would sometimes carry wedged blocks called chalks,
Speaker 1: just like you would have for an airplane, and you
Speaker 1: would actually there's footage of people who were driving cars
Speaker 1: around that time who would jump out of their car
Speaker 1: with these wooden blocks, run behind the cars it's starting
Speaker 1: to roll backward, and try to wedge those blocks behind
Speaker 1: the wheels so that the car wasn't rolling backward anymore.
Speaker 1: The external brakes also had no protection against dirt and
Speaker 1: other debris, so they would get dirty and they would
Speaker 1: wear down relatively quickly, which would necessitate frequent maintenance or
Speaker 1: replacement of those brakes. The internal drum braking systems were
Speaker 1: protected from debris and dirt right because they're inside the drum,
Speaker 1: so that stuff wasn't getting to them. Although as you
Speaker 1: use the drum brakes over and over over again, they
Speaker 1: do develop dust inside the drum itself because it's actually
Speaker 1: wearing away both the brake pads and the inside of
Speaker 1: the drum. You know that friction is slowly grinding away
Speaker 1: some of that material. But also because of the design,
Speaker 1: the shoes inside a drum could maintain pressure for as
Speaker 1: long as the brake was engaged, which meant there was
Speaker 1: no need to worry about rolling backward down the hill.
Speaker 1: If you had the brake pressed, then you know it
Speaker 1: wasn't unwinding. If it was an internal drum brake, the
Speaker 1: brakes would last longer than external breakes, but they weren't
Speaker 1: as effective at stopping the vehicle as quickly, so for
Speaker 1: that reason, some car manufacturers chose to employ both types
Speaker 1: of brakes on the rear wheels of vehicles, in particular,
Speaker 1: so that both an external and internal drum brake system
Speaker 1: could work together from the same press of a brake pedal.
Speaker 1: In those early systems, everything was purely mechanical. We haven't
Speaker 1: gotten to the hydraulic sections yet, so that meant that
Speaker 1: it was using stuff like cables and rods and levers
Speaker 1: to do mechanical work and to move these different elements
Speaker 1: to where they needed to be. Eventually that gave way
Speaker 1: to hydraulic systems, but will have a different type of
Speaker 1: break to talk about first before we get into hydraulics.
Speaker 1: So that means we need to get back to Sperry's
Speaker 1: disc brakes. His implementation didn't get much traction, and yes
Speaker 1: that's a pun, but others began to work on similar designs,
Speaker 1: possibly with complete independence and without knowledge of Sperry's work, because,
Speaker 1: like I said, a lot of people were working on
Speaker 1: this at the same time. Uh. One of those was
Speaker 1: an inventor named F. W. Lanchester in the UK who
Speaker 1: received a patent in nineteen o two for a mechanical
Speaker 1: approach to the disc brake design, so instead of the
Speaker 1: electromagnetic approach, the calipers would be controlled by a cable.
Speaker 1: The cable, when pulled taught, would force the calipers closed.
Speaker 1: But lanchester solution wasn't ideal. The disc mounted to the
Speaker 1: wheel hub was made of metal, which makes sense, but
Speaker 1: the brake pads that were actually on the caliper were
Speaker 1: made out of copper, So when you were applying a break,
Speaker 1: that meant that you were applying to copper pads on
Speaker 1: either side of a rapidly spinning metal disc. And as
Speaker 1: you might imagine, this created no small amount of noise.
Speaker 1: From what I understand, it was the type of high pitched,
Speaker 1: screeching noise that was not that different from what you
Speaker 1: might get with fingernails dragged down a chalkboard, so not
Speaker 1: a pleasant sound. In addition, the brake pads would wear
Speaker 1: down very quickly and had the same issues with dart
Speaker 1: and debris that the external drum systems had, so lanchester
Speaker 1: solution was, like Sperry's, largely unimplemented. A dude named Fruit
Speaker 1: made the next big contribution. His name is Herbert Fruit.
Speaker 1: He was an English engineer who took the brake pads
Speaker 1: and lined them with a substance that would cut back
Speaker 1: on that noise. It was a long lasting material that
Speaker 1: could withstand a lot of abuse, and it would become
Speaker 1: a common brake pad material for both disc brakes and
Speaker 1: drum brakes, and still is used in a lot of
Speaker 1: breaks today. That material was asbestos. Yikes, So asbestos was
Speaker 1: long considered a truly remarkable substance with a ton of
Speaker 1: practical applications. It's actually a group of silicate minerals, it's
Speaker 1: not just one, and this group all have similar traits
Speaker 1: their fibrous which means you can actually draw the stuff
Speaker 1: out and create a material that's similar in consistency to
Speaker 1: cotton balls in a way. Its heat resistant, it's an
Speaker 1: electrical insulator, and it holds up against a lot of
Speaker 1: otherwise corrosive chemicals, so it can make other stuff stronger
Speaker 1: when you mix the substances together, and it was a
Speaker 1: common additive for everything from cement to paper. But what
Speaker 1: was not known for a very long time was that
Speaker 1: asbestos is actually incredibly toxic. Now, as I said, it's fibrous,
Speaker 1: and so they are these tiny asbestos fibers in the
Speaker 1: mineral and these can easily be swallowed or inhaled without
Speaker 1: your knowledge. Their microscopic in size, so you're not able
Speaker 1: to spot them. And due to those qualities I mentioned earlier,
Speaker 1: the fact that the fibers are so resistant to so
Speaker 1: many different things, it also means that they can last
Speaker 1: indefinitely inside a person's body and there's no real way
Speaker 1: to flush them out. They don't dissolve, and these trapped
Speaker 1: fibers can cause inflammation and even much worse problems genetic
Speaker 1: damage to cells. Uh they can lead to development of cancer.
Speaker 1: The illnesses take a really long time to develop, too,
Speaker 1: like between twenty to fifty years, which is one of
Speaker 1: the reasons asbestos remained in popular use for so long.
Speaker 1: It took ages to figure out that it was hazardous
Speaker 1: in the first place because the effects took so long
Speaker 1: to manifest. Now, nearly all the auto manufacturers in the
Speaker 1: United States stopped making asbestos brake pads in the ninety nineties,
Speaker 1: but there are a lot of aftermarket companies that continue
Speaker 1: to do so, largely manufacturing in places like China and
Speaker 1: India and Mexico. So to this day, there are aftermarket
Speaker 1: brake pads that have potentially dangerous amounts of asbestos in them. Now,
Speaker 1: that probably doesn't pose a huge health hazard to the
Speaker 1: average driver, but it is a concern for mechanics. For
Speaker 1: people who work on break systems regularly, that's something that
Speaker 1: they should actively be concerned about and protect themselves against.
Speaker 1: Because there's no telling if someone's getting cheap break pads
Speaker 1: from overseas, because you know there they are much less
Speaker 1: expensive than buying them here Domestically, there's a chance that
Speaker 1: one of the materials in there is asbestos and it
Speaker 1: could be in a concentration high enough for it to
Speaker 1: be a danger. So just to be aware if you
Speaker 1: happen to be someone who works on such things, just
Speaker 1: you know, you need to just be care full. We're
Speaker 1: masks and stuff. Now. I've got a lot more to
Speaker 1: say about breaks, including the introduction of hydraulics and modern
Speaker 1: breaking systems, but first let's take another quick break. Now,
Speaker 1: it didn't take long for engineers to look into hydraulics
Speaker 1: to work with car brakes. Cars were getting heavier and faster,
Speaker 1: which meant the brake systems needed to be up to
Speaker 1: the task of bringing these increasingly speedy hunks of metal
Speaker 1: to a stop. In nineteen eighteen, Malcolm Lockheed actually law
Speaker 1: feed at the time, began to experiment with hydraulics. So
Speaker 1: what exactly is a hydraulic system and why is it important? Well,
Speaker 1: hydraulics is a branch of science that is really about
Speaker 1: the practical applications of fluids, typically liquids. It's largely, but
Speaker 1: not exclusively, about how those fluids moved through systems like pipes, channels,
Speaker 1: and tanks. Blaze Pascal and Daniel Bernoulli first worked out
Speaker 1: the basic principles of fluid dynamics and hydraulic power. But
Speaker 1: people had been making practical use of fluids for some
Speaker 1: time already, So this was one of those things where
Speaker 1: people had figured out that they could could use fluids
Speaker 1: to do work, but no one had quite worked out
Speaker 1: the science behind it yet until Pascal and Bernoulli came along.
Speaker 1: Pascal figured out that a pressure in an incompressible liquid
Speaker 1: transmits equally in all directions, and this law ends up
Speaker 1: being incredibly useful if you want to leverage fluids to
Speaker 1: do work. Bernoulli's last data that energy and a fluid
Speaker 1: remains constant, but that changing things like the diameter of
Speaker 1: a pipe will change the pressure in a system. The
Speaker 1: energy remains the same, but the flow slows down as
Speaker 1: it encounters a larger diameter, and the surface area of
Speaker 1: the fluid presses against is increased. And effectively, what that
Speaker 1: means is you can create mechanical advantage through hydraulic systems.
Speaker 1: So if we have a closed system with income rescible fluid,
Speaker 1: so you if you push against the fluid, you can't
Speaker 1: compress it to a smaller form. It's going to push
Speaker 1: against all areas equally. We can actually transfer force from
Speaker 1: one side of a system to another, with the liquid
Speaker 1: acting as the carrier for that force. And by changing
Speaker 1: the sizes of cylinders and pistons, you can also amplify
Speaker 1: force by trading force for distance, kind of similar to
Speaker 1: what we were doing when we were talking about levers.
Speaker 1: So let's say we've got two pistons connected in a
Speaker 1: hydraulic system. It's much easier to understand if we take
Speaker 1: a concrete example, or at least a hypothetical example. So
Speaker 1: we've got piston one. Piston one is two inches in
Speaker 1: diameter or one inch radius. That's a five point eight
Speaker 1: centimeters in diameter. Piston two is six inches in diameter
Speaker 1: or fifteen point to four centimeters in diameter. So then
Speaker 1: we have to figure out the area of these two
Speaker 1: p stance and area of a circle is pie times
Speaker 1: the radius squared, So piston one has the radius of
Speaker 1: one inch. One inch squared is one one times pie
Speaker 1: is three point one four, etcetera, etcetera. So we just
Speaker 1: will simplify to say three point one four is the
Speaker 1: area of our first piston. Our second piston has an
Speaker 1: area of twenty eight point two six because it's much larger.
Speaker 1: So that means piston two is nine times the size
Speaker 1: of piston one in area. If we apply a force
Speaker 1: to piston one in this closed system where we have
Speaker 1: liquid acting as the uh the transmission force between one
Speaker 1: piston and the other. So we push a piston one down,
Speaker 1: we're gonna get nine times that force on piston two.
Speaker 1: So if we push down on piston one with one
Speaker 1: pounds of force, it makes piston two go up. Nine
Speaker 1: hundred pounds of force because piston two is nine times
Speaker 1: the size of piston one. However, there is a tradeoff.
Speaker 1: That tradeoff is in the distance traveled by the each piston.
Speaker 1: Piston two will travel one ninth the distance of piston one.
Speaker 1: So in order to make piston two rise up one inch,
Speaker 1: you would have to push piston one down nine inches
Speaker 1: push down piston one nine inches into a cylinder at
Speaker 1: one dred pounds of pressure. Piston two will lift up
Speaker 1: one inch with nine hundred pounds of pressure, so you
Speaker 1: amplify the force you decrease the distance. Lackeed's method, in
Speaker 1: which hydraulic pressure would create the force that would push
Speaker 1: a brake shoe against the brake drums, wasn't embraced immediately.
Speaker 1: According to Popular Mechanics, the first passenger car to have
Speaker 1: four wheel hydraulic brakes was the Model A Dusenberg in
Speaker 1: nineteen twenty one. A decade later, a handful of car
Speaker 1: manufacturers were using hydraulics and the brake systems, but the
Speaker 1: rest were still relying on cable brakes. Ford would be
Speaker 1: the last of the major manufacturers to make the switch
Speaker 1: to hydraulics, and that happened in nineteen thirty nine. Going
Speaker 1: back just a bit in n another advance helped make
Speaker 1: hydraulic disc brakes practical. It was the power assist technology,
Speaker 1: and that would reduce the physical effort a driver would
Speaker 1: have to exert to apply the brakes. So if you
Speaker 1: didn't have power assist, you would find that you have
Speaker 1: to push that brake pedal really hard in order to stop.
Speaker 1: So instead of having to really stomp on the brake pedal,
Speaker 1: the driver just uses a little effort and the car
Speaker 1: itself would help to do the rest. The N Pierce
Speaker 1: arrow used vacuum that was generated by the inlet manifold
Speaker 1: of the engine to offset the physical force required by
Speaker 1: the driver. Diesel powered cars, by the way, actually require
Speaker 1: a secondary vacuum pump to generate the vacuum necessary for
Speaker 1: the power assiste because their engines don't work the same
Speaker 1: way anyway. Describing how all this works is tri key
Speaker 1: without using visual aids. It involves a diaphragm that initially
Speaker 1: has a partial vacuum on either side of the diaphragm,
Speaker 1: but when you press the brake pedal, it opens up
Speaker 1: a valve on the vacuum booster side. Of the diaphragm
Speaker 1: and increases the pressure on that side and thus gives
Speaker 1: the boost to the driver who's pushing down on the brake.
Speaker 1: To understand this, I really recommend looking at the article
Speaker 1: how power brakes work on the House Stuff Works site,
Speaker 1: because like I said, it's really hard to describe just
Speaker 1: in audio alone and haven't make any sense. But the
Speaker 1: point is this was one of those necessary features to
Speaker 1: make hydraulic brakes practical to remove some of that effort
Speaker 1: that was required in order to push down on the brake.
Speaker 1: Oh and and hey, remember when I talked about the
Speaker 1: lever at the top of the episode and how the
Speaker 1: distances between a force of fulcrum and a load can
Speaker 1: affect how much force you apply on the system. The
Speaker 1: same is true with brake pedals. Brake pedals are actually levers,
Speaker 1: their class two levers, so the distance the pedal has
Speaker 1: to travel tends to be much greater than the distance
Speaker 1: from the pedal cylinder to the pivot, so the force
Speaker 1: of the pedal will be multiplied at the point of
Speaker 1: the cylinder. So these are all both These are all
Speaker 1: like mechanical ways to make it easier to actually apply
Speaker 1: the brakes physically easier. Typically, a hydraulic brake system has
Speaker 1: one master cylinder, so this is the one that's actually
Speaker 1: controlled by your brake pedal. The pedal cylinder with a
Speaker 1: piston that connects via a rod to the brake pedal,
Speaker 1: so it's like a direct line from the brake pedal
Speaker 1: through a rod to the the actual piston for the
Speaker 1: master cylinder. There's usually some more complicated stuff in there now,
Speaker 1: especially for modern vehicles, but this is the basic idea.
Speaker 1: Each wheel on a car tends to have its own
Speaker 1: secondary cylinder, sometimes called a slave cylinder, the master cylinder
Speaker 1: and the slave cylinders. The master cylinder tends to be
Speaker 1: smaller than the slave cylinders, so we get that force
Speaker 1: amplification effect I just talked about. This is what allows
Speaker 1: the brakes to apply enough force to slow down a
Speaker 1: massive vehicle traveling at high speeds, just from a human
Speaker 1: stepping down on a brake pedal. Alright, so we've covered
Speaker 1: drum brakes, which you can still find on many car
Speaker 1: models on the rear wheels, and we've covered disc brakes,
Speaker 1: which were adopted quickly in Europe and later in America
Speaker 1: and tend to be the brake system used for front wheels.
Speaker 1: Both systems now rely on hydraulics to transmit force from
Speaker 1: the brake pedal to the brakes attached to the respective
Speaker 1: wheels to those those UH brake shoes or the brake calipers.
Speaker 1: There's also the emergency brake, which may have a physical
Speaker 1: cable attached to a brake shoe UH that in turn
Speaker 1: is attached to one or more wheels. And there's one
Speaker 1: other advance I feel like I should cover, and that's
Speaker 1: anti lock braking systems or a B s. What are
Speaker 1: they and how do they work well? A skidding wheel
Speaker 1: has less traction and a non skidding wheel, and a
Speaker 1: skidding wheel is one in which the patch of tire
Speaker 1: in contact with the road is sliding relative to that
Speaker 1: road and the wheel the tire itself is not rotating anymore.
Speaker 1: It's locked. So if you can break a car without
Speaker 1: locking the tire, like without locking the wheels down entirely,
Speaker 1: but rather applying pressure so that the wheels are slowed
Speaker 1: to a stop, you're in better shape. You're not gonna
Speaker 1: skid out and have a terrible accident, or at least
Speaker 1: you won't have a terrible accident in that way. This
Speaker 1: is particularly important on slippery road conditions, and that's what
Speaker 1: a b S or anti lock brake systems do so.
Speaker 1: And a b S has four main additional components on
Speaker 1: top of the regular brake system. You have speed sensors
Speaker 1: that's what's monitoring the speed of rotation of the wheels.
Speaker 1: You have a set of valves, you have pump, and
Speaker 1: you have a controller. The sensors are pretty self explanatory,
Speaker 1: Like I said, they monitor the wheels. They live for
Speaker 1: signs that the wheel is about to lock into position,
Speaker 1: which means the wheel would actually stop spinning entirely. The
Speaker 1: sensors may be located at each wheel, or it might
Speaker 1: be located at the differential. The valves are meant to
Speaker 1: control break pressure from the master cylinder, so the master
Speaker 1: cylinders providing the pressure for the overall brake system. A
Speaker 1: valve can be open and thus send pressure onto the
Speaker 1: brake system as per normal. So in other words, it's
Speaker 1: it's almost as if the valve is not even there.
Speaker 1: It could be closed and block the hydraulics from going
Speaker 1: to the break from the master cylinder. This would be
Speaker 1: for each individual wheel would have its own so it's
Speaker 1: not like one for all four wheels. It's one for
Speaker 1: each wheel, so in that case, the hydraulic fluid would
Speaker 1: essentially bypass that wheels brake system, and then the valve
Speaker 1: has a third position to release some of the pressure
Speaker 1: from the brake system. Now, because there's a pressure release system,
Speaker 1: the a B S needs a pump to build pressure
Speaker 1: up again, and the controller is essentially the brains, it's
Speaker 1: in charge of the whole thing. The controller sends signals
Speaker 1: to decrease or increase break pressure to individual wheels to
Speaker 1: avoid lock up, while still allowing for deceleration. The hydraulic
Speaker 1: system begins to pulse a bit as this happens, which
Speaker 1: can feel a little weird if you if you're not
Speaker 1: used to it, and those that pulse can be fast.
Speaker 1: It can be like fifteen times per second with some vehicles.
Speaker 1: A BS doesn't magically make cars safer in all conditions,
Speaker 1: but they do come in really handy, as I said,
Speaker 1: in those slippery road conditions, so they do have a
Speaker 1: real benefit. But that does not mean that a BS
Speaker 1: is magically going to make every driver safer. There are
Speaker 1: possible problems that you can encounter. So, for one example,
Speaker 1: when you're breaking with a system that doesn't have anti
Speaker 1: lock brakes, you can't steer while you're breaking. Steering is
Speaker 1: locked with a b S, you can still steer while
Speaker 1: you're breaking, and sometimes that I can actually lead to
Speaker 1: drivers making bad decisions and steering off the road. There's
Speaker 1: a lot more that we could say about break systems
Speaker 1: and newer innovations in the space. Uh there are some
Speaker 1: high tech things that we can cover, but I think
Speaker 1: I'm going to save that for another episode. We'll we'll
Speaker 1: talk more in detail about some cutting edge materials and
Speaker 1: techniques and breaking sometime down the line, but for now,
Speaker 1: let's put us stop to this. If you guys have
Speaker 1: suggestions for future topics for tech stuff, why not write
Speaker 1: me and let me know The email addresses tech stuff
Speaker 1: at how stuff works dot com or pop on by
Speaker 1: our website. The u r L for that is text
Speaker 1: stuff podcast dot com. You'll find links there to our
Speaker 1: social media as well as to the merchandise store. Remember
Speaker 1: every purchase you make goes to help the show, and
Speaker 1: we greatly appreciate it. And I'll talk to you again
Speaker 1: really soon for more on this and bathans of other topics.
Speaker 1: Because it how staff works dot com really really wonder