WEBVTT - TechStuff Pumps the Brakes 0:00:04.120 --> 0:00:07.160 Get in touch with technology with tech Stuff from how 0:00:07.200 --> 0:00:14.000 stuff works dot com. Hey there, and welcome to tech Stuff. 0:00:14.040 --> 0:00:17.760 I'm your host, Jonathan Strickland. I'm an executive producer with 0:00:17.880 --> 0:00:20.000 How Stuff Works, and I heart radio and I love 0:00:20.079 --> 0:00:23.320 all things tech. And you know, we've been going pretty 0:00:23.360 --> 0:00:27.200 fast with tech stuff over the past I don't know, decade, 0:00:27.840 --> 0:00:31.159 So I felt maybe it was time to apply the 0:00:31.320 --> 0:00:34.800 brakes a little bit. I don't mean to slow down 0:00:34.840 --> 0:00:37.880 the show or stop it, but rather to take time 0:00:37.920 --> 0:00:41.280 to talk about how breaks work and the science surrounding breaks, 0:00:41.960 --> 0:00:46.040 because puns are sort of a thing I do, but seriously, 0:00:46.280 --> 0:00:47.840 I thought this would give us a chance to talk 0:00:47.880 --> 0:00:51.440 about mechanical and hydraulic systems as well as the science 0:00:52.000 --> 0:00:57.600 that's behind breaking, the physics that are involved. So first, 0:00:57.920 --> 0:01:00.640 let's talk about what makes breaks no necessary in the 0:01:00.640 --> 0:01:03.600 first place, which is pretty obvious stuff, but it leads 0:01:03.720 --> 0:01:07.800 into a discussion about physical forces that guided the whole 0:01:07.800 --> 0:01:13.840 evolution of breaks. So, a body in motion has momentum. 0:01:14.080 --> 0:01:18.120 Momentum is a quantity of movement. It depends upon two things, 0:01:18.600 --> 0:01:22.080 the mass of the object that's in motion and how 0:01:22.160 --> 0:01:25.840 quickly that mass is moving. So really comes down to 0:01:25.920 --> 0:01:29.039 how much of the stuff is there and how fast 0:01:29.200 --> 0:01:33.039 is it going. A simple equation would be momentum equals 0:01:33.480 --> 0:01:38.039 mass times velocity. So if you have something with a 0:01:38.200 --> 0:01:41.920 low mass, like a bullet, but it's traveling at a 0:01:42.040 --> 0:01:45.240 high velocity, it has a pretty good amount of momentum. 0:01:45.560 --> 0:01:49.240 If you have something that's really really huge, like a glacier, 0:01:49.440 --> 0:01:53.360 but it's moving incredibly slowly, it still has a lot 0:01:53.360 --> 0:01:57.280 of momentum, because momentum depends upon both the mass and 0:01:57.320 --> 0:01:59.680 the velocity, not just one or the other. Now, if 0:01:59.680 --> 0:02:02.160 you have something that's of a pretty decent size, like 0:02:02.200 --> 0:02:04.840 a vehicle, and it's moving at a pretty good speed, 0:02:05.480 --> 0:02:08.800 then that has got a lot of momentum too. And 0:02:09.120 --> 0:02:13.120 that's a problem, right If you've got a mass that's 0:02:13.120 --> 0:02:15.720 moving at a pretty good speed and you need to 0:02:15.760 --> 0:02:18.320 stop that mass, you have to figure out how do 0:02:18.360 --> 0:02:22.280 you offset that momentum, How do you convert this movement 0:02:22.400 --> 0:02:26.480 energy into something else. So momentum is also a vector 0:02:26.560 --> 0:02:31.200 quantity vectors and physics have not just a magnitude but 0:02:31.400 --> 0:02:36.160 also a direction. Acceleration is the same. It has a 0:02:36.160 --> 0:02:39.800 magnitude and a direction. So to fully describe momentum, we 0:02:39.840 --> 0:02:43.000 need not just how many kilograms of mass are traveling 0:02:43.000 --> 0:02:46.320 at a speed typically in meters per second, but also 0:02:46.360 --> 0:02:49.880 the direction of travel. Now, a body and motion has 0:02:49.960 --> 0:02:54.080 kinetic energy as well. So to reduce momentum and stop 0:02:54.160 --> 0:02:57.760 a body in motion, you need to convert that kinetic energy, 0:02:57.840 --> 0:03:02.160 that energy of movement in to something else. Because we 0:03:02.200 --> 0:03:06.200 have to remember the laws of conservation, the laws of 0:03:06.200 --> 0:03:09.320 the universe. We we energy cannot be created, it cannot 0:03:09.360 --> 0:03:13.280 be destroyed. We cannot just make energy, we cannot destroy energy. 0:03:13.320 --> 0:03:17.440 We can convert it from one form into another. So 0:03:17.560 --> 0:03:21.359 breaks do this by converting the kinetic energy of an 0:03:21.400 --> 0:03:26.720 object in motion into heat through friction. And you've probably 0:03:26.800 --> 0:03:30.040 heard the term waste heat. Now what we mean by 0:03:30.080 --> 0:03:32.480 that is that we've got some sort of system. It 0:03:32.520 --> 0:03:36.240 can be pretty much any given mechanical system in particular, 0:03:36.280 --> 0:03:40.520 but really other systems as well, biological systems. Uh So, 0:03:40.560 --> 0:03:44.040 it could be pretty much anything. And in this system, 0:03:44.240 --> 0:03:47.600 some of the energy that we're depending on is going 0:03:47.680 --> 0:03:49.920 not to whatever it is we're trying to do, but 0:03:50.120 --> 0:03:53.800 rather into generating heat. So with a bicycle, some of 0:03:53.800 --> 0:03:57.840 the energy we're putting forth by peddling is not going 0:03:57.880 --> 0:04:00.840 directly to making us move we're losing it in the 0:04:00.880 --> 0:04:04.800 form of friction, and thus heat um really the heat 0:04:04.840 --> 0:04:07.760 that's generated from friction. That's the best way of putting it. 0:04:08.160 --> 0:04:11.440 The heat represents energy that we could not otherwise exploit 0:04:11.600 --> 0:04:13.760 for whatever it is we're trying to do. So here's 0:04:13.800 --> 0:04:17.279 another example, with an electrical generator. We might say that 0:04:17.320 --> 0:04:21.280 the friction of the moving parts inside that electrical generator 0:04:21.600 --> 0:04:24.720 means that some of the kinetic energy we would otherwise 0:04:24.839 --> 0:04:28.440 use to create more electricity is instead converting to heat, 0:04:28.960 --> 0:04:32.200 and that heat isn't being captured in any meaningful way. 0:04:32.279 --> 0:04:37.159 So the work we did two direct this kinetic energy 0:04:37.240 --> 0:04:40.920 to the generator was wasted. Some of that work we 0:04:40.920 --> 0:04:44.880 weren't able to get efficiency. So no system is perfect. 0:04:45.040 --> 0:04:47.760 Any system with moving parts is going to have friction 0:04:47.839 --> 0:04:50.040 to deal with. And there are a lot of super 0:04:50.040 --> 0:04:53.279 smart materials scientists out there who have worked really hard 0:04:53.680 --> 0:04:57.080 to develop stuff that generates very little friction, and that 0:04:57.279 --> 0:05:00.240 is in an effort to increase efficiency and minim eyes 0:05:00.279 --> 0:05:03.360 waist heat. But when it comes to breaks, we want 0:05:03.440 --> 0:05:07.280 that friction. That's what is stopping an object. So we 0:05:07.360 --> 0:05:11.640 need something that is really good at creating this friction. 0:05:11.680 --> 0:05:14.400 We want to convert that kinetic energy into heat and 0:05:14.440 --> 0:05:18.720 thus decrease the momentum of a fast moving massive object, 0:05:19.040 --> 0:05:21.479 perhaps even bringing that object to a complete stop, not 0:05:21.600 --> 0:05:24.200 just slowing it down, but stopping it. So in the 0:05:24.320 --> 0:05:29.480 very early days of break systems, even before there were cars, 0:05:30.040 --> 0:05:33.200 you were looking at a pretty simple device. And this 0:05:33.240 --> 0:05:36.000 would be in the horse drawn carriage era. You've got 0:05:36.040 --> 0:05:39.599 a carriage that's being pulled by horses. Even when the 0:05:39.600 --> 0:05:41.920 horses start to slow down, you know you still have 0:05:42.000 --> 0:05:44.640 the momentum of the actual carriage itself. You need to 0:05:44.680 --> 0:05:48.599 slow down the carriage uh to to come to a stop. 0:05:48.640 --> 0:05:52.400 So the break was typically a lever, and the long 0:05:52.520 --> 0:05:55.400 end of the lever was extended up towards the driver. 0:05:55.520 --> 0:05:57.720 That was the handle side, So the longside of the 0:05:57.800 --> 0:05:59.800 lever is the handle. On the short end of the 0:06:00.000 --> 0:06:04.640 ever was a wooden block. The wooden block was when 0:06:04.680 --> 0:06:07.800 you pull, the lever, would make contact, typically with the 0:06:07.880 --> 0:06:11.640 driver's side front wheel of the carriage to create that 0:06:11.720 --> 0:06:14.599 source of friction and convert the kinetic energy of the 0:06:14.640 --> 0:06:18.600 turning wheel into heat and thus slow and eventually stop 0:06:18.760 --> 0:06:22.479 the carriage. A lever is one of the classic simple 0:06:22.600 --> 0:06:26.279 machines it's a bar that rotates around the fulcrum, and 0:06:26.320 --> 0:06:29.200 a fulcrum is just a fixed point. So the length 0:06:29.279 --> 0:06:32.880 of the lever on either side of the fulcrum determines 0:06:32.960 --> 0:06:36.000 the amount of effort or force exerted or acquired per side. 0:06:36.360 --> 0:06:40.640 In a classic class one lever, lever makes certain types 0:06:40.680 --> 0:06:43.479 of work, such as lifting, easier by reducing the workload 0:06:43.880 --> 0:06:47.159 that is needed to affect a change to to create 0:06:47.200 --> 0:06:51.000 that lift. There are three classes of levers, and I 0:06:51.080 --> 0:06:53.840 just mentioned class one lever. That's the one where you've 0:06:53.880 --> 0:06:56.920 got a force that's applied on one end of the lever, 0:06:57.760 --> 0:07:00.400 you have a load the thing you're trying to move 0:07:00.720 --> 0:07:03.680 or activate on the other end of the lever, and 0:07:03.760 --> 0:07:07.680 the fulcrum is somewhere in between those two. If it's 0:07:07.680 --> 0:07:11.200 in the center of the bar, then the fulcrum ends 0:07:11.280 --> 0:07:14.280 up balancing loads on either side. If you put equal 0:07:14.360 --> 0:07:17.280 loads on either side, it should just balance out, kind 0:07:17.280 --> 0:07:19.320 of like you know, just a scale if you think 0:07:19.320 --> 0:07:21.320 of it that way. So a see saw or a 0:07:21.320 --> 0:07:24.280 teeter totter would be an example of a class one lever. 0:07:25.160 --> 0:07:26.960 If two people weigh the same on a seesaw, it 0:07:26.960 --> 0:07:29.320 balances out. But if you put a heavier person on 0:07:29.320 --> 0:07:31.320 one end and a lighter person on the other. The 0:07:31.320 --> 0:07:33.840 heavier person sinks down the lighter person goes up into 0:07:34.120 --> 0:07:37.560 the air. But if the heavier person were to scoot 0:07:37.720 --> 0:07:42.560 forward on the seesaw to decrease the space between the 0:07:42.560 --> 0:07:46.360 heavier person and the fulcrumb, then you would eventually balance out. 0:07:46.400 --> 0:07:49.800 And if the heavier person kept scooting forward to get 0:07:49.800 --> 0:07:53.120 closer to the fulcrum, the lighter person would eventually sink 0:07:53.200 --> 0:07:55.160 to the bottom and the heavier person would be up 0:07:55.160 --> 0:08:01.360 in the air. So by decreasing the disc dins between 0:08:01.440 --> 0:08:06.160 the load and the fulcrum, you can increase the the 0:08:06.200 --> 0:08:09.880 lifting power essentially, or the really you're decreasing the amount 0:08:09.880 --> 0:08:12.320 of force needed to lift that load, if you're really 0:08:12.320 --> 0:08:15.080 thinking about it that way, you're creating a mechanical advantage. 0:08:16.000 --> 0:08:18.160 But there are two other classes of levers. I should 0:08:18.160 --> 0:08:22.240 probably cover those because some of them actually factor into 0:08:22.280 --> 0:08:25.800 breaks as well later down the line. Class two levers 0:08:26.160 --> 0:08:29.520 put the fulcrum on one end of a bar, so 0:08:29.720 --> 0:08:32.000 instead of it being in the middle, somewhere the fulcrum 0:08:32.080 --> 0:08:34.120 the fixed point is actually on one end of the bar. 0:08:34.600 --> 0:08:36.400 The load is somewhere in the middle of the bar 0:08:36.720 --> 0:08:39.040 and the force is at the far into the bar. 0:08:39.720 --> 0:08:42.880 So a wheelbarrow is this type of lever, because these 0:08:42.920 --> 0:08:45.600 can be kind of difficult to imagine otherwise. But if 0:08:45.600 --> 0:08:49.839 you think about the wheel on a wheelbarrow is a fulcrum, 0:08:49.920 --> 0:08:52.960 and you put a load of stuff into the wheelbarrow itself, 0:08:53.520 --> 0:08:55.559 and then you lift the other side of the wheelbarrow 0:08:55.600 --> 0:08:57.920 by the handles. So the closer the load is to 0:08:57.960 --> 0:09:00.679 the fulcrum, the more the mechanical advantage you will have 0:09:01.360 --> 0:09:04.400 uh and the less you will the less effort you'll 0:09:04.440 --> 0:09:08.000 need to lift the handles for a given load. Or 0:09:08.480 --> 0:09:10.560 you can think of it another way, the heavier the 0:09:10.600 --> 0:09:12.800 load you will be able to manage as long as 0:09:12.840 --> 0:09:16.120 it's closer to the fulcrum. A class three lever has 0:09:16.160 --> 0:09:19.480 the fulcrum on one end, the load at the other end, 0:09:19.720 --> 0:09:22.160 and the lifting force is in the middle. Now, these 0:09:22.240 --> 0:09:25.760 leavers don't provide mechanical advantage, but they can increase the 0:09:25.800 --> 0:09:29.600 speed at which a force moves a load. A baseball 0:09:29.640 --> 0:09:32.000 bat would be an example of this, or even your 0:09:32.240 --> 0:09:34.200 your own forearm would be an example of this. But 0:09:34.240 --> 0:09:37.439 we're gonna leave the off from here because class three 0:09:37.520 --> 0:09:41.800 leavers don't really factor into the discussion for breaking, So 0:09:41.840 --> 0:09:44.280 the wooden block break is a Class one lever. On 0:09:44.280 --> 0:09:46.720 one end is the wooden block, its position near the 0:09:46.760 --> 0:09:49.520 carriage wheel. A little bit further up from the wooden 0:09:49.520 --> 0:09:53.319 block is the fulcrum, the fixed point closer to the 0:09:53.320 --> 0:09:56.200 wooden block than to the handle, and the other end 0:09:56.200 --> 0:09:58.680 of the lever, the long end has the handle, so 0:09:58.760 --> 0:10:01.600 the handle must travel a radar distance than the wooden block. 0:10:02.000 --> 0:10:04.600 When you pull back on the brake um, you are 0:10:04.640 --> 0:10:08.920 pulling the breakback much further than the wooden block has 0:10:08.960 --> 0:10:12.240 to travel to make contact with the the carriage wheel. 0:10:12.960 --> 0:10:15.559 But by increasing that distance, you reduce the amount of 0:10:15.600 --> 0:10:17.920 work you need to do on the force end to 0:10:17.960 --> 0:10:20.760 get a result on the load end. Uh. This is 0:10:20.800 --> 0:10:23.680 important because if you're going pretty fast and you need 0:10:23.720 --> 0:10:26.520 to slow down that wheel, you need to exert a 0:10:26.559 --> 0:10:29.920 good deal of force to create enough friction and convert 0:10:29.960 --> 0:10:34.120 that kinetic energy into heat. You couldn't easily do that 0:10:34.200 --> 0:10:36.679 if you were, let's say, just holding a wooden block 0:10:37.240 --> 0:10:40.559 and just trying to push the wooden block directly against 0:10:40.640 --> 0:10:43.240 the carriage wheel. You probably wouldn't be able to do 0:10:43.280 --> 0:10:46.360 that with enough force. To make a difference in a 0:10:46.360 --> 0:10:48.640 sufficient amount of time. By putting it on this lever, 0:10:49.160 --> 0:10:52.080 you can increase the amount of force you're exerting on 0:10:52.160 --> 0:10:56.400 the wheel itself on the carriage wheel through pressure with 0:10:56.480 --> 0:10:58.480 this wooden block, then you would if you were to 0:10:58.480 --> 0:11:01.520 do it directly. So the lever makes the job easier. 0:11:02.720 --> 0:11:07.720 Very important part of physics in general. The brake system 0:11:07.760 --> 0:11:10.800 made the transition from horse drawn carriages to some of 0:11:10.840 --> 0:11:13.440 the earliest automobiles in the nineteenth century, and it was 0:11:13.800 --> 0:11:15.880 the same sort of thing. They were using wooden blocks. 0:11:16.240 --> 0:11:20.640 The wheels on these early automobiles were often metal. There 0:11:20.960 --> 0:11:25.200 was no rubber tires yet, and they worked reasonably well 0:11:25.360 --> 0:11:28.840 under certain conditions, namely that the vehicles were traveling at 0:11:28.880 --> 0:11:31.920 slower speeds were talking below twenty miles per hour or 0:11:31.960 --> 0:11:36.480 below thirty two kilometers per hour, and traffic was pretty 0:11:36.600 --> 0:11:39.240 light in those days, so there weren't a lot of 0:11:40.000 --> 0:11:42.600 incidents where you would need to break quickly due to 0:11:42.920 --> 0:11:46.560 an increased amount of traffic on the streets. But you 0:11:46.600 --> 0:11:50.320 also weren't necessarily uh, it wasn't necessarily a good idea 0:11:50.360 --> 0:11:53.240 to go, like driving a car up a steep hill, 0:11:53.360 --> 0:11:57.920 for example, because your breaking system was pretty primitive. The 0:11:57.960 --> 0:12:00.120 only way you would prevent yourself from rolling backwards was 0:12:00.120 --> 0:12:05.280 either by applying more acceleration to overcome the force of 0:12:05.320 --> 0:12:09.240 gravity that's pulling you down, or to hold a break 0:12:09.840 --> 0:12:15.120 real strong against that wheel so that you're not slipping backward. Uh. 0:12:15.160 --> 0:12:18.319 This also was probably a good thing. Like that, It's 0:12:18.320 --> 0:12:20.720 probably a good thing you weren't going very fast, not 0:12:20.840 --> 0:12:24.960 just because the brakes were primitive, but because those wheels 0:12:25.000 --> 0:12:27.760 were metal. You would feel it when you would run 0:12:27.840 --> 0:12:30.440 over bumps in the road, of which there were many. 0:12:31.000 --> 0:12:33.680 It was very similar to if you remember my episodes 0:12:33.720 --> 0:12:37.280 about the history of the bicycle, the bone shaker, that 0:12:37.280 --> 0:12:40.360 it was a nickname for a type of early bicycle 0:12:40.520 --> 0:12:44.640 that was really uncomfortable to ride. It was a very uh, 0:12:44.840 --> 0:12:48.520 stiff ride, you might say. But it was clear the 0:12:48.600 --> 0:12:53.520 lever approach wasn't going to remain sufficient as cars were 0:12:53.520 --> 0:12:56.960 getting faster and heavier and traffic was increasing. You could 0:12:56.960 --> 0:12:59.520 stop a faster car with a lever breake, but it 0:12:59.520 --> 0:13:03.200 would take longer as you converted that kinetic energy into 0:13:03.200 --> 0:13:07.560 heat through friction, so you didn't come to a stop 0:13:07.679 --> 0:13:11.040 in as reasonable amount of space. You know, and an 0:13:11.080 --> 0:13:13.480 increase in traffic, you had a decreased the email of 0:13:13.520 --> 0:13:17.320 time you had in order to slow down to avoid collisions. 0:13:17.360 --> 0:13:20.040 So something had to change. A couple of people came 0:13:20.120 --> 0:13:25.280 up with some very clever alternatives. One was a proposal 0:13:25.440 --> 0:13:29.200 that was made. It was actually not just proposed, it 0:13:29.240 --> 0:13:33.320 was developed. It was the creation of Elmer Ambrose Sperry 0:13:33.520 --> 0:13:38.840 of Cleveland, Ohio. Sperry's solution involved using disc brakes. Now 0:13:38.840 --> 0:13:41.360 I'm going to cover modern disc brakes a little later 0:13:41.360 --> 0:13:44.000 in this episode, but it's good to just go ahead 0:13:44.040 --> 0:13:46.800 and then explain what the general idea was because it 0:13:46.840 --> 0:13:51.000 remained the same even later on. So let's say you've 0:13:51.040 --> 0:13:53.360 got a wheel, and you've got that hub of the wheel. 0:13:53.440 --> 0:13:57.200 This is part that turns on the axle. Attached to that, 0:13:57.520 --> 0:14:01.400 you have a disk that is really just part of 0:14:01.440 --> 0:14:04.200 the hub of the wheel, but it's separate from the tire. 0:14:04.640 --> 0:14:08.760 So you've got this free standing disc. Positioned over this 0:14:08.800 --> 0:14:12.120 disc is a set of calipers, so that either side 0:14:12.160 --> 0:14:15.120 of the caliper are on either side of the disk, 0:14:15.480 --> 0:14:18.200 and it can pinch down on the disk, just like 0:14:18.280 --> 0:14:21.880 your fingers would pinch down if you had let's say 0:14:21.920 --> 0:14:26.640 a spinning frisbee between two fingers and you rut uh. 0:14:26.680 --> 0:14:29.040 You know, your friend is holding their two fingers together, 0:14:29.600 --> 0:14:32.040 and the frisbee is spinning around on the axle of 0:14:32.040 --> 0:14:35.120 those two fingers. If you brought your fingers like calipers, 0:14:35.200 --> 0:14:37.600 right on the gadge and then pinched, you could stop 0:14:37.600 --> 0:14:40.920 the frisbee and its spin. That's the same idea as 0:14:41.000 --> 0:14:46.440 this set of disc brakes the the In a sense, 0:14:46.440 --> 0:14:48.480 it's working very similar to the way the wooden block 0:14:48.600 --> 0:14:51.440 that would press directly against the wheel itself works, except 0:14:51.480 --> 0:14:54.880 instead of of hitting the wheel, you're hitting this disc 0:14:54.960 --> 0:14:59.200 that's attached to the wheel. Um. Pretty clever. And Sperry 0:14:59.360 --> 0:15:02.880 was working on an early electric vehicle. You may remember 0:15:02.920 --> 0:15:05.000 in some of my previous episodes, I've talked about how 0:15:05.080 --> 0:15:10.520 electric cars actually pre date internal combustion engine cars. The 0:15:10.600 --> 0:15:16.280 earliest automobiles were electric vehicles, not not gasoline powered vehicles. 0:15:16.320 --> 0:15:18.560 So he's working on this electric car, and he was 0:15:18.600 --> 0:15:23.240 actually using electro magnetism to close those calipers, to shut them, 0:15:23.880 --> 0:15:26.320 to attract the pincher to the disk and have it 0:15:26.760 --> 0:15:31.640 clamped tight enough to start to break the wheel. Uh. 0:15:31.960 --> 0:15:36.680 Springs that were attached to the calipers would create the 0:15:36.680 --> 0:15:39.240 force that would allow the calipers to open up again 0:15:39.280 --> 0:15:41.840 once the electro magnetic field went away. So if you 0:15:41.880 --> 0:15:45.160 were to step on a brake in Sperry's design, you 0:15:45.200 --> 0:15:48.640 would cause a current to flow through the braking system, 0:15:48.640 --> 0:15:52.920 thus generating the electromagnetic field and forcing the calipers closed 0:15:53.440 --> 0:15:57.280 and breaking the disk, breaking b R A K I, 0:15:57.520 --> 0:16:02.080 n G. The disk. Letting the foot pedal brake would 0:16:02.080 --> 0:16:05.360 interrupt the current, so the field would dissipate, the springs 0:16:05.400 --> 0:16:08.120 on the caliper would pull the caliper open again. It 0:16:08.200 --> 0:16:13.160 was a very ingenious creation, but Sperry's invention didn't catch 0:16:13.280 --> 0:16:15.760 on in the States. A similar idea would take off 0:16:15.760 --> 0:16:18.800 in Europe, however, and I'll talk about a different breaking 0:16:18.800 --> 0:16:22.120 system that would see early success in the United States, 0:16:22.400 --> 0:16:25.160 and that early success would extend all the way into 0:16:25.280 --> 0:16:28.680 the modern day. But I'll do that in just a second. First, 0:16:29.040 --> 0:16:39.960 let's take a quick break. So right around the same 0:16:40.000 --> 0:16:44.760 time Sperry was working on the disc brake solution, Gottlieb 0:16:44.920 --> 0:16:48.600 Daimler was developing a different approach called the drum brake. 0:16:49.400 --> 0:16:52.240 Daimler's idea was to attach a drum mounted on an 0:16:52.280 --> 0:16:56.320 axle and to wrap a cable around that drum and 0:16:56.560 --> 0:17:00.120 pulling the brake would create tension on the cable, tightening 0:17:00.200 --> 0:17:03.680 it around the drum and creating the friction needed to 0:17:03.760 --> 0:17:06.880 slow and then stop a vehicle. So if you can 0:17:06.960 --> 0:17:10.199 think of maybe a spinning axle and then wrapping a 0:17:10.240 --> 0:17:13.320 belt around it and then pulling the belt, really taught 0:17:13.520 --> 0:17:17.320 so that that creates that friction and then slowing the 0:17:17.359 --> 0:17:19.840 axle down. It's similar to that. So you have this 0:17:19.920 --> 0:17:23.359 dedicated drum for this purpose. UH. This was an idea 0:17:23.480 --> 0:17:27.119 that will Helm Maybach used in nineteen o one in 0:17:27.200 --> 0:17:31.160 some early Mercedes designs, but it was Louis Renault who 0:17:31.280 --> 0:17:35.679 defined the drum break as a standard in vehicles. It 0:17:35.760 --> 0:17:40.920 was Renault's UH design that really took off. That being said, 0:17:41.119 --> 0:17:43.480 there are also a ton of different mechanics and engineers 0:17:43.520 --> 0:17:45.800 working on this problem, and so the idea may have 0:17:45.800 --> 0:17:50.199 been developing in parallel around the world. Renault gets the 0:17:50.200 --> 0:17:53.600 credit for making this the first really practical drum break, 0:17:54.480 --> 0:17:57.000 but lots of people were working on this because the 0:17:57.000 --> 0:18:00.960 automobile was a rising technology at the time. Now, the 0:18:01.080 --> 0:18:04.480 drum brake is a pretty clever invention, and a modernized 0:18:04.600 --> 0:18:08.359 version is still used in many vehicles today, though typically 0:18:08.400 --> 0:18:12.119 only for the rear wheels for most passenger vehicles. It 0:18:12.240 --> 0:18:15.000 was also the dominant form of breaking systems in the 0:18:15.080 --> 0:18:18.960 United States until the nineteen seventies, though in Europe things 0:18:18.960 --> 0:18:23.080 were a little different. The original drum brakes weren't great 0:18:23.400 --> 0:18:28.720 on flat surfaces. These drum brakes that had a a 0:18:28.720 --> 0:18:32.679 a belt or a strip of metal or something wrapped 0:18:32.720 --> 0:18:35.920 around a drum that would then tighten to slow things down, 0:18:36.280 --> 0:18:39.439 those worked fine on flat surfaces. A break race in 0:18:39.560 --> 0:18:43.440 nineteen o two pitted a horse drawn coach that had 0:18:43.480 --> 0:18:49.200 a lever style break against a Victoria horseless carriage that 0:18:49.280 --> 0:18:52.560 had an internal drum brake, and a custom vehicle that 0:18:52.680 --> 0:18:55.879 was created by a guy named Ransom E. Olds And 0:18:55.920 --> 0:19:01.200 he called it the Oldsmobile. Yep, that's where that comes from. So, 0:19:01.600 --> 0:19:03.280 like I said, the coach had a tire break, the 0:19:03.320 --> 0:19:06.240 horseless carriage had an internal drum break, which I'll talk 0:19:06.240 --> 0:19:09.200 about in a second, and the Oldsmobile had a different 0:19:09.280 --> 0:19:12.560 drum brake design that used a band of stainless steel 0:19:13.200 --> 0:19:16.640 wrapped around the drum. So pressing on the brake pedal 0:19:16.840 --> 0:19:20.840 rather than pulling a lever would contract this band. So 0:19:20.880 --> 0:19:23.600 that would grip the drum more tightly and thus create 0:19:23.680 --> 0:19:26.600 the friction. The oldsmobile proved it could stop in less 0:19:26.640 --> 0:19:30.480 time and thus travel the least distance while breaking than 0:19:30.520 --> 0:19:33.600 the other two vehicles. So this meant that for a while, 0:19:33.880 --> 0:19:37.120 external breaks, in which the breaking mechanism is on the 0:19:37.160 --> 0:19:41.480 outside of the drum, were more popular, but both external 0:19:41.520 --> 0:19:44.680 and internal drum breaking systems existed at the same time. 0:19:45.040 --> 0:19:49.239 So what was an internal drum break system. Well, in 0:19:49.240 --> 0:19:52.720 that case, you have the drum assembly that's mounted on 0:19:52.760 --> 0:19:55.960 a wheel or an axle, So just think of it's 0:19:55.960 --> 0:19:59.760 almost like a pot, right, It's just mounted on there 0:19:59.800 --> 0:20:03.760 and and everything is inside this pot. So you have 0:20:03.840 --> 0:20:08.760 these extendable parts inside the drum. They're called shoes. And 0:20:08.800 --> 0:20:12.800 these extendable shoes are anchored with respect to the car, 0:20:12.880 --> 0:20:17.240 so they are not rotating. They are stationary with respect 0:20:17.359 --> 0:20:20.960 to the chassis of the vehicle. So the drum rotates 0:20:21.119 --> 0:20:26.639 around these shoes as as the cars in motion. The 0:20:26.760 --> 0:20:30.840 shoes have breaking material, so a material meant to generate 0:20:30.920 --> 0:20:36.680 friction coding the surface of the shoe itself the stopping surface. 0:20:37.000 --> 0:20:39.399 So when you engage the brake, when you step on 0:20:39.520 --> 0:20:44.199 the brake, pedal A system extends these shoes on the 0:20:44.240 --> 0:20:47.760 inside of the drum, so that that breaking surface is 0:20:47.880 --> 0:20:51.840 rubbing up against the inside edge of that rotating drum. 0:20:52.160 --> 0:20:54.200 So it's the same effect that you were getting before, 0:20:54.320 --> 0:20:58.760 this idea of pressing a surface against a moving object 0:20:59.080 --> 0:21:02.560 in order to generate friction and convert kinetic energy into heat. 0:21:02.800 --> 0:21:06.320 It's just in this case it's happening on the inside 0:21:06.960 --> 0:21:11.040 of a rotating surface, not on the outside of the 0:21:11.160 --> 0:21:16.760 rotating surface. Uh. The this is really interesting stuff. It's 0:21:16.800 --> 0:21:20.639 a little difficult to envision just from my audio, I imagine, 0:21:21.000 --> 0:21:23.919 but if you really want to look into this and 0:21:23.960 --> 0:21:26.800 see some diagrams and some animations and things like that, 0:21:27.200 --> 0:21:30.280 How Stuff Works has several articles about breaks, including how 0:21:30.359 --> 0:21:33.520 drum brakes work, and that's incredibly useful. So if you 0:21:33.560 --> 0:21:37.520 want to check in on a visual aid, I highly 0:21:37.560 --> 0:21:40.760 recommend that I don't write for How Stuff Works anymore, 0:21:41.080 --> 0:21:43.800 but I still respect the heck out all the articles 0:21:43.800 --> 0:21:46.240 that are on that site. They are incredibly useful, especially 0:21:46.400 --> 0:21:48.800 for stuff like this, to get an understanding of these 0:21:48.840 --> 0:21:53.720 mechanical systems. So in addition, uh, these brakes would typically 0:21:53.760 --> 0:21:57.240 have some sort of cable or belt wrapped around the drum. 0:21:57.280 --> 0:21:59.240 So you would have a lot of cars that would 0:21:59.280 --> 0:22:01.080 have kind of a high red system where they have 0:22:01.160 --> 0:22:06.199 both external and internal breaking UH systems incorporated into the 0:22:06.320 --> 0:22:12.840 same overall brake system and create more friction more more efficiently, 0:22:13.000 --> 0:22:15.320 so that you could convert that kinetic energy into heat 0:22:15.359 --> 0:22:19.359 and stop faster. Now, early on, the external drum brake 0:22:19.480 --> 0:22:22.479 systems were believed to be superior. They could stop a 0:22:22.480 --> 0:22:27.120 car faster and less time less distance than internal ones, 0:22:27.200 --> 0:22:30.600 but they did have some big drawbacks. One of those 0:22:30.680 --> 0:22:33.240 was that the brakes would tend to unwind if you 0:22:33.320 --> 0:22:36.560 try to stop halfway up a hill. So you you're driving, 0:22:37.040 --> 0:22:39.160 you got a hill. Let's say you're in San Francisco. 0:22:39.200 --> 0:22:42.399 That's a great example. You're in San Francisco, you hit 0:22:42.440 --> 0:22:44.760 a hill, you're driving up the hill, and then you're 0:22:44.760 --> 0:22:48.080 coming up to an intersection where you have to stop. Well, 0:22:49.160 --> 0:22:53.760 that was an issue because the brakes would unwind. At 0:22:53.800 --> 0:22:56.720 that point. Gravity would create a backward pull on the 0:22:56.760 --> 0:23:00.159 car to pull it back down the hill, and that 0:23:00.160 --> 0:23:03.520 would cause the bands wrapped around the drum to unwind 0:23:03.520 --> 0:23:06.320 in the car would actually start to roll backwards. For 0:23:06.359 --> 0:23:11.360 that reason, early motorists would sometimes carry wedged blocks called chalks, 0:23:12.080 --> 0:23:15.119 just like you would have for an airplane, and you 0:23:15.160 --> 0:23:18.720 would actually there's footage of people who were driving cars 0:23:18.760 --> 0:23:21.400 around that time who would jump out of their car 0:23:21.560 --> 0:23:24.600 with these wooden blocks, run behind the cars it's starting 0:23:24.640 --> 0:23:27.720 to roll backward, and try to wedge those blocks behind 0:23:27.760 --> 0:23:31.200 the wheels so that the car wasn't rolling backward anymore. 0:23:32.040 --> 0:23:35.080 The external brakes also had no protection against dirt and 0:23:35.119 --> 0:23:37.440 other debris, so they would get dirty and they would 0:23:37.440 --> 0:23:41.159 wear down relatively quickly, which would necessitate frequent maintenance or 0:23:41.240 --> 0:23:45.640 replacement of those brakes. The internal drum braking systems were 0:23:45.640 --> 0:23:48.920 protected from debris and dirt right because they're inside the drum, 0:23:49.240 --> 0:23:53.200 so that stuff wasn't getting to them. Although as you 0:23:53.359 --> 0:23:57.080