WEBVTT - How Does A Bicycle Balance? 0:00:08.200 --> 0:00:10.280 Hey, orror, Hey, what image do you get in your 0:00:10.280 --> 0:00:13.960 mind if I say the phrase mysteries of the universe? 0:00:15.360 --> 0:00:17.840 I think I think of you know, black holes and 0:00:17.960 --> 0:00:20.439 what's inside of them, and what happened at the beginning 0:00:20.480 --> 0:00:23.240 of time and where is the universe going to go? 0:00:23.560 --> 0:00:26.079 Those are all wonderful mysteries, and I'd love to dig 0:00:26.120 --> 0:00:28.400 into them. But what if I told you you don't 0:00:28.400 --> 0:00:32.000 have to go so far away to find mysteries. M 0:00:32.960 --> 0:00:36.360 You mean, like, why is a cartoonists hosting a podcast 0:00:36.360 --> 0:00:40.800 about science? Yeah, that's exactly the point. It turns out 0:00:41.240 --> 0:00:45.080 that there are deep unanswered physics questions all around us. 0:00:45.120 --> 0:00:46.559 You don't have to travel to the edge of the 0:00:46.560 --> 0:00:49.599 galaxy to find something we don't understand. Yeah, I've heard 0:00:49.600 --> 0:00:51.920 about this that in the objects we use every day 0:00:51.960 --> 0:00:55.520 there might be things that even physicists don't know how 0:00:55.560 --> 0:00:58.080 it works. Yeah, it turns out physicists don't know what 0:00:58.120 --> 0:01:00.360 we're talking about all the time, but you don't know 0:01:00.360 --> 0:01:02.480 what you're talking about, or you know what you're talking about, 0:01:02.480 --> 0:01:05.760 but you don't understand. No, that's the exact job of 0:01:05.800 --> 0:01:08.319 physics is to look around us and say, do we 0:01:08.520 --> 0:01:11.400 really know how this works? Can we actually understand it, 0:01:11.440 --> 0:01:13.880 and sometimes we think it's a simple explanation, but we 0:01:13.920 --> 0:01:15.600 sit down to work it out and it turns out 0:01:15.680 --> 0:01:19.080 it's much more complicated than we thought. Yeah, it turns 0:01:19.080 --> 0:01:22.200 out there are big mysteries even in the things that 0:01:22.480 --> 0:01:26.200 a lot of us ride to work every day. That's right. 0:01:41.959 --> 0:01:45.319 I'm and I'm Daniel, and welcome to our podcast Daniel 0:01:45.360 --> 0:01:49.080 and Jorge Explain the Universe, a production of I Heart Radio, 0:01:49.280 --> 0:01:51.880 in which we look around for weird things in the 0:01:51.960 --> 0:01:54.720 universe that don't make sense and try to explain them 0:01:54.720 --> 0:01:57.880 to you. Sometimes we look far, sometimes we look pretty 0:01:57.880 --> 0:02:00.320 close to home. That's right. Today in the episod, we're 0:02:00.360 --> 0:02:03.200 going to try something a little bit different. So usually 0:02:03.280 --> 0:02:05.920 we talk about the big things out there in the universe, 0:02:05.960 --> 0:02:09.320 all the big fundamental questions about what the universe is 0:02:09.360 --> 0:02:11.960 made out of and where's it going and what happens 0:02:11.960 --> 0:02:15.360 inside of crazy things like black holes. But today we're 0:02:15.440 --> 0:02:18.160 going to try something a little different. That's right. Some 0:02:18.240 --> 0:02:21.040 of those are big sexy questions that affect the human 0:02:21.080 --> 0:02:23.320 condition and the context of your life. But we think 0:02:23.800 --> 0:02:26.320 sometimes there are mysteries of physics right here in front 0:02:26.360 --> 0:02:28.600 of us that can give us deep insights into the 0:02:28.600 --> 0:02:31.400 way things work and how we live our lives. So 0:02:31.440 --> 0:02:34.040 this might be the first of a series of episodes 0:02:34.040 --> 0:02:37.440 in which we tackle a question that's kind of close 0:02:37.520 --> 0:02:41.240 to us or in maybe hidden in everyday objects. That's right, 0:02:41.280 --> 0:02:44.280 So look around you think about whether you understand the 0:02:44.320 --> 0:02:46.760 way the world works around you. Why doesn't your house 0:02:46.800 --> 0:02:49.799 fall down? How do the lightning rods work? All these 0:02:49.800 --> 0:02:51.880 things that are happening around you. Do you really know 0:02:51.919 --> 0:02:54.600 how they work? Do physicists even know how they work? 0:02:54.840 --> 0:02:57.360 So today on the podcast, we're going to talk about 0:03:02.320 --> 0:03:05.640 why don't bicycles fall over? You know, the bicycle has 0:03:05.639 --> 0:03:07.880 been around for a long time. People have been putting 0:03:07.919 --> 0:03:10.280 their butts on those funny seats and peddling around for 0:03:10.360 --> 0:03:13.360 decades and decades and decades. But the physics of a 0:03:13.400 --> 0:03:16.960 bicycle is fascinating. If you just hold a bicycle and 0:03:17.080 --> 0:03:20.079 let go, it's going to fall over, right, But if 0:03:20.080 --> 0:03:23.360 you push your bicycle so that's going fast, it doesn't 0:03:23.400 --> 0:03:26.040 fall over. It can ride by itself. It's kind of 0:03:26.040 --> 0:03:28.079 a ridiculous situation. Do you think about it? Like? Who 0:03:28.160 --> 0:03:32.440 thought it to take two wheels and right around and 0:03:32.919 --> 0:03:35.520 in them? That's right? It seems like it wouldn't balance, right. 0:03:35.520 --> 0:03:37.520 It seems much more natural to have three wheels or 0:03:37.520 --> 0:03:40.080 four wheels. Right. Maybe somebody was just short of wheels 0:03:40.120 --> 0:03:42.160 and they were like, dang it, I ordered three wheels 0:03:42.160 --> 0:03:44.160 on the internet, only to arrive. I guess I'm gonna 0:03:44.160 --> 0:03:47.360 have to invent something. They couldn't aford a third wheel 0:03:49.560 --> 0:03:51.440 only they only had the raw materials enough for two 0:03:51.480 --> 0:03:54.120 wheels or something. You were like inventing a new myth 0:03:54.200 --> 0:03:57.160 of the genesis of the bicycle, right, Yeah, well it 0:03:57.280 --> 0:04:00.240 seems implausible because it's hard to balance, right. You need 0:04:00.280 --> 0:04:02.920 at least, you know, like a chair needs at least 0:04:02.960 --> 0:04:06.800 three legs to stand on. It's kind of weird to 0:04:06.840 --> 0:04:09.720 think that someone would think of a vehicle that only 0:04:09.800 --> 0:04:11.920 rides on two wheels. Yeah, that's right. Not many people 0:04:11.960 --> 0:04:14.800 invent chairs with just two legs, right, for that same reason. 0:04:15.000 --> 0:04:19.200 That would be pretty odd. Um. Yeah, there's so there's 0:04:19.240 --> 0:04:21.760 two wheels, all these two wheel contraptions. We have motorcycles, 0:04:21.800 --> 0:04:24.400 we have bicycles. It is amazing. It's not something that 0:04:24.440 --> 0:04:27.200 I would have considered inventing, but it works. You see 0:04:27.240 --> 0:04:30.960 bikes everywhere, and you go to Europe and India, and China, 0:04:31.040 --> 0:04:33.800 and there's all over the world. There's thousands and millions 0:04:33.800 --> 0:04:36.359 and millions of bicycles being used every day, but the 0:04:36.400 --> 0:04:38.760 physics of it is still a bit of a mystery. Yeah, 0:04:38.800 --> 0:04:41.960 how do bicycles stay up? Apparently physicists don't really have 0:04:42.000 --> 0:04:45.880 a good answer, right, yeah, that's right, Um, it's it's fascinating. 0:04:45.920 --> 0:04:48.040 But you know, do this experiment in your head. You 0:04:48.080 --> 0:04:52.440 remember riding a bike, probably, and it's the faster you go, 0:04:52.600 --> 0:04:55.159 the more stable the bike. Seems that at some point 0:04:55.560 --> 0:04:58.160 you could even lean back and take your hands off 0:04:58.200 --> 0:05:00.960 the handlebars, and it seems like a ridiculous thing to do. 0:05:01.000 --> 0:05:03.240 You're going twenty miles an hour and if the if 0:05:03.240 --> 0:05:06.440 the handlebars flipped over, you would fly over the front 0:05:06.480 --> 0:05:09.479 of the bike. You can hurt yourself. But miraculously, almost 0:05:09.880 --> 0:05:12.360 it seems pretty stable. And I remember discovering this as 0:05:12.360 --> 0:05:14.640 a kid, that you could ride your bike without holding 0:05:14.640 --> 0:05:17.920 onto the handlebars because at high speeds it's so stable. Yeah, 0:05:17.960 --> 0:05:20.640 wearing a helmet though, right, we should probably wearing a helmet, 0:05:20.680 --> 0:05:23.039 and it's only you know, off the street. Of course, 0:05:23.279 --> 0:05:26.080 never ride with without holding the handlebars on the street 0:05:26.080 --> 0:05:31.680 because you could cause an accident or or okay, that's right. Actually, 0:05:31.680 --> 0:05:34.640 my dad used to commute to work on a bicycle, 0:05:35.160 --> 0:05:36.920 and we lived up in the mountains in New Mexico, 0:05:37.040 --> 0:05:39.400 and so he could get pretty snowy, and I remember 0:05:39.480 --> 0:05:43.359 that he would put um nails and studs in his 0:05:43.400 --> 0:05:46.520 wheels on purpose, like sticking out so that he could 0:05:46.520 --> 0:05:49.960 grip the ice. Yeah, he was a pretty hardcore commute 0:05:49.960 --> 0:05:51.479 commute to work. He was like, I'm going to commute 0:05:51.520 --> 0:05:53.880 to work no matter what the weather is. Sounds like 0:05:53.880 --> 0:05:57.880 a Matt Mag's modification there. Yeah. I asked him once 0:05:57.920 --> 0:05:59.400 if it was good for the ice, and he said, actually, 0:05:59.400 --> 0:06:03.760 it's pretty good for pedestrians too. Let's getting for clearing 0:06:03.760 --> 0:06:09.240 the road on pedescans exactly exactly. Um, yeah, so we 0:06:09.360 --> 0:06:12.680 understand that, but we don't understand why bikes stand up. Yeah, 0:06:12.720 --> 0:06:14.520 it's kind of a mystery. You write it, and uh, 0:06:14.560 --> 0:06:16.280 I mean you do. You're doing a lot of the 0:06:16.520 --> 0:06:20.760 balancing with your handlebars, right, But a lot of the 0:06:20.880 --> 0:06:23.120 balancing and staying up is kind of done for you 0:06:23.160 --> 0:06:25.440 when you're riding a bicycle. Yeah, that's right. A lot 0:06:25.440 --> 0:06:27.520 of it is done for you. And I think there's 0:06:27.520 --> 0:06:30.159 also a fascinating area there where your brain has like 0:06:30.240 --> 0:06:34.839 incorporated the mechanics of a bicycle into your into itself. Right. 0:06:34.880 --> 0:06:36.760 It's like learning how to ride a bike is basically 0:06:36.839 --> 0:06:39.760 learning how to map where you want the bike to 0:06:39.800 --> 0:06:41.560 go to, how to how to move your hands and 0:06:41.880 --> 0:06:44.480 shift your weight, etcetera to ride the bike. Right. It's 0:06:44.480 --> 0:06:47.160 amazing seeing seeing a kid learn to do that. It's 0:06:47.320 --> 0:06:50.360 really complicated thing. Like imagine a robot learning to ride 0:06:50.360 --> 0:06:53.200 a bicycle. That's a really hard task. That's something that 0:06:53.279 --> 0:06:56.560 robots still can't do because it's very counterintuitive, right to 0:06:56.640 --> 0:06:59.360 ride a bicycle. Yeah, that's right. I mean like if 0:06:59.360 --> 0:07:01.480 you're starting to into the right, then you actually you'll 0:07:01.520 --> 0:07:05.320 have to teach your body to turn the wheel towards 0:07:05.320 --> 0:07:08.159 the right to balance, Yeah, exactly, And you have to 0:07:08.240 --> 0:07:09.880 lean the just the right way, and sometimes you have 0:07:09.920 --> 0:07:14.080 to lean left to turn right. You can get pretty complicated. Um. 0:07:14.120 --> 0:07:16.680 It's sort of in its most extreme form in those 0:07:16.760 --> 0:07:20.320 crazy motorcycle races. You see those guys whizzing around turns 0:07:20.440 --> 0:07:23.160 like a hundred something miles an hour and their bikes 0:07:23.160 --> 0:07:25.920 are leaning so far over that their knees almost scrape 0:07:25.960 --> 0:07:29.560 the ground. Right. But basically, if you're at home, and 0:07:29.600 --> 0:07:31.680 maybe you don't have a lot of experience of bicycles 0:07:31.720 --> 0:07:35.040 and trying this experiment at home. Borrow a bicycle or 0:07:35.200 --> 0:07:38.240 if you have one, take it out and then hold 0:07:38.280 --> 0:07:40.600 it out either on the street or on the sidewalk, 0:07:40.800 --> 0:07:43.320 or maybe ideally kind of in a little bit of 0:07:43.320 --> 0:07:45.600 a downhill, and then just give it a big push 0:07:45.600 --> 0:07:48.920 forward and you'll see that the bike keeps going straight. 0:07:48.920 --> 0:07:52.760 It doesn't immediately fall over exactly. And so that's the 0:07:52.800 --> 0:07:55.160 topic we want to address today. Why does the bike 0:07:55.400 --> 0:07:59.040 stay up? And so before we dug into it, I thought, well, 0:07:59.120 --> 0:08:01.520 let's find out what people think. Let's see what people 0:08:01.560 --> 0:08:04.360 think the answer might be. Yeah, so you went to 0:08:04.480 --> 0:08:08.840 your local mecca of bicycles right at college campus. That's right, 0:08:09.480 --> 0:08:12.920 that's right, and asked people on the street. Actually, today's 0:08:12.920 --> 0:08:16.320 a sort of a special edition because this quarter at 0:08:16.320 --> 0:08:21.000 you see Irvine, I'm teaching freshman physics, which is mechanics, 0:08:21.080 --> 0:08:24.360 And the week before we did these interviews, I just 0:08:24.400 --> 0:08:28.640 taught about rotation incular momentum, and so my students were 0:08:28.680 --> 0:08:31.640 primed for this topic, and so I asked students in 0:08:31.720 --> 0:08:34.640 my freshman physics class this question. So the interviews you'll 0:08:34.720 --> 0:08:37.839 hear are with students in my class. Cool. So think 0:08:37.840 --> 0:08:39.600 for a moment and if you think you know the 0:08:39.600 --> 0:08:42.880 answer why a bicycle stays upright? So think about it 0:08:42.880 --> 0:08:46.000 for a second and then listen to these answers. Here's 0:08:46.000 --> 0:08:49.760 what they had to say. Why does a bicycle balance? Oh, 0:08:49.840 --> 0:08:52.480 you have to get the motion going. You gotta get 0:08:52.800 --> 0:08:58.760 you know, centrifugal forces. You gotta get your back are 0:08:58.800 --> 0:09:03.559 your physics professor, And definitely not. Would it be because 0:09:03.600 --> 0:09:06.280 since there's two wheels like the force, and one goes 0:09:06.320 --> 0:09:09.360 to thegether, that's why it still keeps going forward. Something 0:09:09.400 --> 0:09:16.920 like that. Okay, thanks, umws. There's a talk from the 0:09:16.960 --> 0:09:22.720 tire um way we're rotated, the talk of support the rotation. 0:09:22.960 --> 0:09:26.600 It's sort okay because it's is it because it's moving? 0:09:27.280 --> 0:09:30.520 Chance because like a loane like standing up and want it. 0:09:30.960 --> 0:09:34.360 They want to like stand up by itself. So I'm 0:09:34.360 --> 0:09:39.840 not sure. Actually I'm not exactly sure, but I'm thinking 0:09:39.880 --> 0:09:42.240 it has something to do with maybe cent tripital forces. 0:09:43.000 --> 0:09:46.800 The fact that there's constantly like pushing in or like 0:09:46.960 --> 0:09:49.920 towards the center of the bicycle wheels, so as opposed 0:09:49.960 --> 0:09:52.440 to where it's not rotating. It's kind of unstable because 0:09:52.440 --> 0:09:55.200 it doesn't have any like other points of contact. I 0:09:55.240 --> 0:09:57.960 think that this has to do with either the angular 0:09:57.960 --> 0:10:01.360 momentum or rotational inertia the bi So if something is 0:10:01.440 --> 0:10:04.439 rotating like a gyroscope, because of its angular momentum, you 0:10:04.520 --> 0:10:08.360 will continue to rotate more easily rather than starting or 0:10:08.400 --> 0:10:12.839 stopping it from rotating. Great, thanks very much, by I 0:10:12.920 --> 0:10:17.400 was moving wise because you're Jesus Christ. It's not because 0:10:17.400 --> 0:10:22.760 of Jesus Christ. Um, I have no idea. Thanks all right. 0:10:22.800 --> 0:10:27.319 So where are you impressed with your students or none impressed? Um? 0:10:27.360 --> 0:10:30.040 I think the scores on the final tell you how 0:10:30.080 --> 0:10:32.960 impressed I should be with these students. Um. Yeah, they 0:10:33.000 --> 0:10:35.880 seem pretty perplexed, like they could not really apply the 0:10:35.920 --> 0:10:40.319 concepts of rotation and anglad momentum to this topic. Um. 0:10:40.360 --> 0:10:42.920 I like how they one of them, even God religious 0:10:43.080 --> 0:10:49.400 di went like Jesus Christ, I don't even know. Um, 0:10:49.400 --> 0:10:51.839 it's tricky. Yeah, it turns out it to be tricky. Um. 0:10:51.880 --> 0:10:54.679 But a few folks, you know, repeated what I think 0:10:54.679 --> 0:10:57.320 a lot of people imagine is the answer, which is 0:10:57.360 --> 0:11:00.320 anglar momentum. Yeah. A lot of people think, oh, it's 0:11:00.320 --> 0:11:03.679 some gyroscope effect, some conservation of angular momentum. Maybe they 0:11:03.679 --> 0:11:05.480 haven't worked through the details in their mind, but that's 0:11:05.480 --> 0:11:08.559 sort of the most common answer. Yeah, I imagine a 0:11:08.600 --> 0:11:10.960 lot of people listen to this podcast. You know, you've 0:11:10.960 --> 0:11:14.120 probably read a few science books maybe or are into signs, 0:11:14.120 --> 0:11:16.160 and you probably think you know the answer. And I 0:11:16.280 --> 0:11:18.439 imagine most people think it's has something to do with 0:11:18.600 --> 0:11:21.640 angular momentum. And so before you click off because you 0:11:21.640 --> 0:11:23.120 think you know the answer, you should know that the 0:11:23.160 --> 0:11:28.640 answer is not angular momentum. You just gave it away. Well, 0:11:28.679 --> 0:11:31.040 I just don't want it to click away. That's right, 0:11:31.480 --> 0:11:35.240 keep listening. Trust us more to it than just angular momentum. 0:11:35.440 --> 0:11:36.920 I mean, it's not even close. It's it's not like 0:11:36.960 --> 0:11:40.080 the dominating factor and why bicycles stay up right. Yeah, 0:11:40.080 --> 0:11:42.280 that's right. But let's stick into a little bit. Let's 0:11:42.320 --> 0:11:45.440 talk about what angle momentum is, how contributes to bikes 0:11:45.440 --> 0:11:47.800 staying upright, and then what else is going on? But 0:11:47.920 --> 0:12:05.320 first a quick break, what exactly is angular momentum? Yeah, 0:12:05.400 --> 0:12:07.240 so let's do it one step a time. Let's just 0:12:07.320 --> 0:12:09.760 make sure we have clear in our heads what momentum is, 0:12:10.000 --> 0:12:13.400 and then we'll extrapolate from that to angular momentum. Right. 0:12:13.440 --> 0:12:16.320 So momentum is just you know, the property of some 0:12:16.440 --> 0:12:20.160 object to keep going when you've pushed it, or to 0:12:21.120 --> 0:12:23.440 you know, not go when you haven't pushed it. It's 0:12:23.480 --> 0:12:26.800 you know, essentially it's the same as inertia, right, Like 0:12:26.840 --> 0:12:29.640 if you if you've got something going, it doesn't let's 0:12:29.679 --> 0:12:32.400 keep it going that it wants to keep going. Yeah, exactly. 0:12:32.880 --> 0:12:35.679 So we say momentum is conserved. That just means if 0:12:35.679 --> 0:12:38.080 something is moving, right, it has a certain amount of momentum. 0:12:38.240 --> 0:12:40.640 That momentum is not going to change unless you apply 0:12:40.679 --> 0:12:43.480 a force to it, right, And that's really what forces are. 0:12:43.559 --> 0:12:47.120 Forces are changes in momentum. And so momentum is just 0:12:47.200 --> 0:12:50.000 this property is something if it's moving, it like sustained movement, 0:12:50.000 --> 0:12:52.360 and it comes it's connected to inertia. It comes from 0:12:52.360 --> 0:12:56.040 the inertia. The mathematical expression for momentum is mass, which 0:12:56.080 --> 0:13:00.000 is inertia times velocity. Right, So something with more mass 0:13:00.040 --> 0:13:03.320 has more inertia and therefore more momentum for the same velocity. 0:13:03.440 --> 0:13:05.360 And that's the weird thing about the universe. Right, Like 0:13:05.400 --> 0:13:09.160 I was talking to a pretty um high level physicism. 0:13:09.200 --> 0:13:11.120 They were saying that we don't really know kind of 0:13:11.160 --> 0:13:14.000 what inertia on. Hold on, you talked to other high levels. 0:13:14.800 --> 0:13:18.360 I'm finding out about this on the podcast What Physics 0:13:18.400 --> 0:13:21.880 Cheating on You? Daniel. Well, okay, I'm putting on my 0:13:21.920 --> 0:13:26.480 two day list, find other cartoonists to talk to. Technically 0:13:26.559 --> 0:13:29.760 happened while we were while we were on a break, Daniel, So, um, 0:13:30.040 --> 0:13:35.360 it's not okay, alright, find flaunch your relationship with other physicists. 0:13:35.400 --> 0:13:37.480 Go ahead, ahead, doesn't hurt my feelings at all. Go ahead. 0:13:38.120 --> 0:13:43.319 It happened before we signed a contract together. Um, but no, no, 0:13:43.600 --> 0:13:46.400 this was this was a lamb gross. He's like the 0:13:46.760 --> 0:13:49.520 one of the head physicist at CERN, right, he is 0:13:49.559 --> 0:13:52.920 a prominent member of the Atlas collaboration and a serious 0:13:52.960 --> 0:13:55.280 Higgs physicists. Yeah, so he's thought a lot about mass. 0:13:55.320 --> 0:13:58.120 That's probably where you're going, he said. Physicists don't really 0:13:58.160 --> 0:14:01.000 know what inertia is, Like why I do things keep 0:14:01.000 --> 0:14:04.040 going the way if you don't apply a course of them. Yeah, 0:14:04.080 --> 0:14:06.680 you're right, it's an observation. Right. We call these things 0:14:06.760 --> 0:14:09.520 laws sometimes as if we like know why they happen 0:14:09.640 --> 0:14:11.480 or why the universe works this way. But a lot 0:14:11.520 --> 0:14:14.240 of times, it's just observation. We're like, well, we noticed this, 0:14:14.640 --> 0:14:17.080 and we'll be able to describe it mathematically and write 0:14:17.080 --> 0:14:19.640 it down. That doesn't mean we know why, right, It 0:14:19.720 --> 0:14:22.240 doesn't mean we couldn't imagine the universe that was different. 0:14:22.520 --> 0:14:25.640 So we don't know why things have inertia. Right. We 0:14:25.760 --> 0:14:28.600 have the Higgs boson, which tells us how things get mass, 0:14:28.920 --> 0:14:30.920 and that tells us where mass comes from. But we 0:14:30.960 --> 0:14:33.440 don't know why mass means inertia, right, We don't know 0:14:33.840 --> 0:14:36.160 how that all works, or like why if we have 0:14:36.240 --> 0:14:40.840 more mass it's harder to stop and or to get going. Yeah, exactly. 0:14:41.040 --> 0:14:44.000 Deep mystery of the universe such a basic question. We 0:14:44.000 --> 0:14:46.840 don't even know how to test it or grapple with it, right, 0:14:47.000 --> 0:14:48.440 So it's just one of those things we just sort 0:14:48.440 --> 0:14:51.280 of accept and move on, and maybe someday somebody's going 0:14:51.320 --> 0:14:54.400 to figure it out, probably by like poking some other mystery, 0:14:54.760 --> 0:14:56.720 maybe even by trying to solve the mystery of an 0:14:56.720 --> 0:15:00.360 everyday object that's around us. Yeah, like the bicycle. Yeah, 0:15:00.440 --> 0:15:03.680 that's why it's important to never let go of mysteries, right, 0:15:03.720 --> 0:15:06.920 even things that seem mundane, right, blenders and bicycles and 0:15:07.000 --> 0:15:09.800 whatever they can hide secrets to the universe. I mean, 0:15:09.840 --> 0:15:12.400 the unicycle, that's all news. But the bicycles where the 0:15:12.760 --> 0:15:21.760 frontier of sciences that that's right, all right, So that's momentum, right. 0:15:21.800 --> 0:15:25.000 People are pretty familiar with momentum. Well, there's another kind 0:15:25.040 --> 0:15:27.840 of momentum, right, Things like to keep moving forward if 0:15:27.880 --> 0:15:30.640 you've pushed them. Things also like to keep spinning, right, 0:15:30.640 --> 0:15:32.960 And that's what we call angular momentum. And this is 0:15:33.000 --> 0:15:35.120 one of my favorite tricks in physics. It's like, let's 0:15:35.120 --> 0:15:38.320 be lazy. Let's not describe something new and with a 0:15:38.360 --> 0:15:41.280 whole new concept. Let's just extrapolate from something else we 0:15:41.320 --> 0:15:44.480 already know. So we have this concept of linear momentum, 0:15:44.720 --> 0:15:46.960 and let's just use the same kind of stuff, the 0:15:47.000 --> 0:15:50.880 same ideas to describe spinning, right. And I think it 0:15:51.120 --> 0:15:54.120 was something that I would always find interesting, is that 0:15:54.240 --> 0:15:57.600 anger momentum is kind of just linear momentum. But if 0:15:57.600 --> 0:15:59.840 you apply to things that are kind of connected to 0:16:00.000 --> 0:16:02.320 each other, right, Like a wheel is really just a 0:16:02.320 --> 0:16:05.040 bunch of atoms stuck together. A wheel is a bunch 0:16:05.080 --> 0:16:07.200 of atoms stuck together. Yes, I can confirm that here 0:16:07.240 --> 0:16:10.040 on the show. I'm getting an update. Yes, yes, yes, 0:16:10.080 --> 0:16:14.520 that's true. The experiment checkt. But what I mean is 0:16:14.560 --> 0:16:16.920 like the angular momentum of a wheel is really just 0:16:16.960 --> 0:16:20.320 a linear momentum of all the particles inside of it, 0:16:20.360 --> 0:16:25.400 but because they're connected together, it sort of becomes becomes 0:16:25.440 --> 0:16:28.800 almost something else. Yeah, that's right. You have all these objects. 0:16:28.840 --> 0:16:30.000 You can think of a wheel is they're just a 0:16:30.040 --> 0:16:32.960 bunch of atoms. But if the atoms weren't connected to 0:16:32.960 --> 0:16:36.080 each other when you spun it, then it wouldn't hold together, right, 0:16:36.120 --> 0:16:38.600 And so it's the bonds between the atoms that hold 0:16:38.600 --> 0:16:41.120 them together. They think of like you know the moon 0:16:41.200 --> 0:16:43.440 going around the Earth, right, why does it move in 0:16:43.480 --> 0:16:45.520 a circle. It moves in a circle because there's a 0:16:45.560 --> 0:16:48.360 force that forces gravity that keeps it from just flying 0:16:48.400 --> 0:16:50.840 off into space. So in the case of the wheel, 0:16:51.240 --> 0:16:53.240 why do the bits of the wheels stay together and 0:16:53.240 --> 0:16:55.360 not just fly off. It's because the atoms are holding 0:16:55.440 --> 0:16:58.120 them together. So, yeah, there's forces they're moving it in 0:16:58.160 --> 0:17:00.800 a circle. But like all things, as you can, you 0:17:00.840 --> 0:17:03.040 can describe it in different levels. Right, you can describe 0:17:03.040 --> 0:17:04.679 it as a single wheel, you can describe it as 0:17:04.840 --> 0:17:08.600 eleven d billion particles. Right. The physics should work in 0:17:08.680 --> 0:17:11.760 every case. It's just sometimes the math is really hairy, 0:17:11.760 --> 0:17:14.240 and sometimes the math is really simple, and so the 0:17:14.280 --> 0:17:18.040 end result is that it behaves as if the spinning 0:17:18.520 --> 0:17:21.280 was like linear momentum. Right, you spin it, it's going 0:17:21.320 --> 0:17:24.600 to keep spinning in space for forever unless you slow 0:17:24.640 --> 0:17:27.119 it down or apply some force or torque to it. 0:17:27.359 --> 0:17:30.359 That's right. Angular momentum is also conserved, right, So if 0:17:30.359 --> 0:17:32.879 something is spinning, it's going to keep spinning until you 0:17:32.880 --> 0:17:36.920 apply the rotational version of force, which we call torque. Right. 0:17:37.400 --> 0:17:40.840 And so that's why, for example, the Moon doesn't fall 0:17:40.880 --> 0:17:44.320 into the Earth right because it has too much angular momentum. Right. 0:17:44.640 --> 0:17:47.360 That's why the solar system hasn't collapsed into a black 0:17:47.440 --> 0:17:50.760 hole because the spinning keeps it from falling in right, 0:17:51.320 --> 0:17:54.360 and so, um, there's lots of consequences of anglid momentum 0:17:54.359 --> 0:17:56.560 and the conservation of angle momentum. So it's definitely a thing. 0:17:56.840 --> 0:17:59.160 Plays a big role in the shape and the structure 0:17:59.240 --> 0:18:01.760 of our of the un verse and our everyday lives. Right. 0:18:02.040 --> 0:18:04.679 So angle momentum is definitely a thing. And it seems 0:18:04.680 --> 0:18:07.360 relevant to the bicycle because the bicycle has big spinning 0:18:07.400 --> 0:18:10.720 things on it, right, right, and angler momentum is also 0:18:10.760 --> 0:18:13.719 kind of different. Not just that it's hard to speed up, 0:18:14.000 --> 0:18:16.000 horror slow down when something is spinning in space, but 0:18:16.040 --> 0:18:19.520 it's kind of hard to change the orientation of it. Right, 0:18:19.520 --> 0:18:22.199 When when something is spinning like a wheel out in space, 0:18:22.840 --> 0:18:25.679 it's kind of hard. It likes to be It likesly 0:18:25.680 --> 0:18:27.719 not just keep spinning, but it likes to keep spinning 0:18:27.800 --> 0:18:30.760 in that direction, that's right. Angler momentum is to find 0:18:31.040 --> 0:18:34.840 along a spin access, right, And just like if you 0:18:34.880 --> 0:18:36.600 push something in a certain direction, it likes to go, 0:18:36.800 --> 0:18:39.880 not just in any direction, but in that direction. If 0:18:39.880 --> 0:18:42.640 you spin something, then it likes to keep spinning around 0:18:42.640 --> 0:18:45.280 the same access of rotation that it started. Yeah, like 0:18:45.359 --> 0:18:48.399 around the same line that goes through the hub of 0:18:48.440 --> 0:18:50.960 the wheel. Yeah, exactly. And so if you have it 0:18:51.080 --> 0:18:53.879 spinning one way and you wanted to spin the other way, right, 0:18:53.920 --> 0:18:56.240 that takes a lot of torque. Or if you have 0:18:56.280 --> 0:18:58.320 it spinning in one direction and you want it spinning 0:18:58.320 --> 0:19:00.920 around an access that's like a rotated by ninety degrees, 0:19:01.280 --> 0:19:04.440 that also takes a lot of torque. Right. So yeah, 0:19:04.480 --> 0:19:06.080 it's not just that it spins. You already likes to 0:19:06.080 --> 0:19:08.160 spin in the same direction. And so that's why people 0:19:08.280 --> 0:19:11.879 assume that's the reason bikes tape upwards, is that up 0:19:11.880 --> 0:19:17.960 boards up right right, upright right, yeah, yeah, exactly, because 0:19:17.960 --> 0:19:20.040 you imagine that this has an application of the bicycle 0:19:20.119 --> 0:19:22.240 that the wheels are spinning, and so the wheels have 0:19:22.280 --> 0:19:25.040 angular momentum, and then the momentum is around the axis 0:19:25.119 --> 0:19:27.960 or the hub around which the wheels are spinning. And 0:19:28.040 --> 0:19:31.439 so if um, if the bike just goes in the 0:19:31.440 --> 0:19:34.920 same direction, then it's going to resist falling over because 0:19:35.000 --> 0:19:38.080 it has some angular momentum around that access. And for 0:19:38.240 --> 0:19:40.840 that for the wheels to spin in another direction would 0:19:40.840 --> 0:19:43.040 require some sort of torque. And it's kind of like 0:19:43.119 --> 0:19:46.320 if you just take one wheel and you roll it 0:19:46.359 --> 0:19:49.600 down the hill or roll it down the street, it's 0:19:49.640 --> 0:19:52.119 gonna mostly stay upright, you know, kind of like a 0:19:52.119 --> 0:19:54.840 coin when you coin plus a coin or roll a 0:19:54.880 --> 0:19:56.520 coin on the table, it just kind of likes to 0:19:56.600 --> 0:19:59.080 keep rolling and stay upright. Yeah. And you can see 0:19:59.080 --> 0:20:00.720 this effect in lots of other of things in your life, 0:20:00.760 --> 0:20:02.679 like if you ever if you ever have like a 0:20:02.680 --> 0:20:06.080 spinning top, right, you know, you can spin a top 0:20:06.119 --> 0:20:08.080 and it will stay upright, and it can even like 0:20:08.160 --> 0:20:10.879 do crazy things like, you know, move you can balance 0:20:10.920 --> 0:20:13.520 it on the tip of your finger, right, um, stuff 0:20:13.560 --> 0:20:16.320 like that. You can never balance a top that wasn't 0:20:16.320 --> 0:20:18.920 spinning on your finger unless you're some sort of magician 0:20:19.000 --> 0:20:21.399 or juggler. But if it's spinning, then it's really pretty 0:20:21.400 --> 0:20:23.760 easy to keep it on your finger. And that's because 0:20:23.760 --> 0:20:27.480 it resists changing its direction because the angle momentum is 0:20:27.480 --> 0:20:30.560 going in a certain direction already. Right, It's the same thing. 0:20:30.640 --> 0:20:33.199 The same effect is in play for the bicycle. And 0:20:33.320 --> 0:20:36.080 if you are a few too too many levels into 0:20:36.080 --> 0:20:40.160 your inception dream, then the top which just keep spinning forever. Right, 0:20:40.320 --> 0:20:42.960 that's right, yeah, exactly, um. And so what happens on 0:20:42.960 --> 0:20:45.879 a bicycle While on a bicycle, for example, if your 0:20:45.880 --> 0:20:50.359 bicycle starts to fall over, right, then the gyroscope effect 0:20:50.400 --> 0:20:53.480 is essentially going to turn the wheel. It's going to 0:20:53.560 --> 0:20:55.720 turn the wheel a little bit in the direction that 0:20:55.760 --> 0:20:58.159 the bike is falling, and that will keep the bike stable. 0:20:58.640 --> 0:21:01.160 So it's not like the gyroscope of keeps the bike 0:21:01.200 --> 0:21:04.240 from leaning over. It's more that it it turns the 0:21:04.280 --> 0:21:06.600