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Vsauce Explains Why Torque is THE Scientific Mystery — Transcript

by More Alex O'Connor · 3,731 words · 617 segments · language en · Watch on YouTube

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0:00Did I hear you once say that you spent a
0:02long time trying to get to the bottom of
0:04like talk?
0:05>> Yeah.
0:05>> And like why it sort of it sort of does
0:08that? Because I feel like a lot of the
0:10time, this is something I really
0:11resonated with because
0:13a lot of the time whenever a scientific
0:15explanation comes along
0:18to you know describe the relations
0:19between objects, there's always this
0:21remaining question of
0:23but why is it doing that?
0:25>> Yeah.
0:25>> So like Isaac Newton, I give this
0:27example all the time.
0:30He discovers gravity, right? And he he
0:32he brilliantly and in an unprecedented
0:35manner describes exactly how planets
0:37relate to each other. He realizes the
0:39same thing that makes this glass fall to
0:40the ground is the same thing that keeps
0:42the the planets in orbit around each
0:44other and there's an inverse square law
0:46that if they're this far away it will be
0:47this amount of mass and this for kind of
0:50attraction.
0:51And he writes all of this in the
0:52Principia Mathematica. And in the
0:53Scholium to the second edition of the
0:56Principia Mathematica
0:57he writes quite explicitly
0:59but as for what this gravity thing
1:02is
1:03as for like why
1:05it does this and why the objects behave
1:07in this way Hypotheses non fingo is what
1:10he writes. I frame no hypothesis. He
1:12doesn't know. He He's got no idea. And I
1:15feel like a lot of the time
1:16that's kind of what's going on in
1:17science. So when I heard you say that
1:18you really wanted to get to the bottom
1:19of talk
1:20>> Yeah.
1:20>> like
1:21I understand that
1:23if I move further away with a long lever
1:25I can apply less force and lift
1:27something heavy, but like
1:28why, right?
1:29>> Yeah.
1:30>> Like
1:32do you think
1:33that
1:34I mean my my feeling is that a lot of
1:37what science does is it just describes.
1:40>> Right.
1:40>> It just describes that if you you know
1:42move further away from the
1:44from the sort of pivot point you'll you
1:46can apply less force and the object will
1:48go up but it doesn't really go much
1:50further to telling you why. But I don't
1:52know if you agree with that assessment
1:53of science.
1:53>> Uh yeah, I mean I agree that
1:56the job of science is to, you know,
1:59describe and predict.
2:00>> Yeah.
2:01>> And so, if I can describe a lever using
2:04a formula,
2:05>> Mhm.
2:05>> I can predict what a lever will do in
2:08the future, and I can build a lever that
2:10will lift something, and it'll work as
2:12soon as I make it.
2:14But then, that's not about asking why it
2:16works.
2:17>> Yeah.
2:17>> Newton was very right to say,
2:20"I don't have an hypothesis for what it
2:22is. I can describe it. I can write
2:24formulas, and you can just plug in
2:26whatever you want. I've condensed all of
2:27this behavior into one equation, but
2:34what is force? It'd be very easy
2:37to have had a totally different history
2:40of science on this planet, where we
2:42never even invented the concept of
2:44force. A force is not a thing.
2:46>> Yeah.
2:46>> I I can't fill this glass up with force.
2:49>> Mhm.
2:49>> Force is really human-centric. It's
2:51about how it feels
2:52>> Exactly.
2:53>> to push something. Um, you could have
2:56just as easily have said, um, "Well,
2:58there's mass and there's acceleration."
3:00>> Mhm.
3:00>> But Newton said, "Ah, but what if
3:03we called their product force?" I mean,
3:05that's what F = MA was. It was a
3:06definition.
3:08>> Yes.
3:08>> "Hold on. Let's just say that there's
3:10this thing called F, and that its
3:11relationship is the product of mass and
3:14acceleration." Is mass is this like
3:16thing that's out there? We don't Today,
3:19we still don't really know. Are there
3:20two kinds of mass?
3:22Is there the the inertial mass and the
3:25gravitational mass? Are those different
3:27things or the same manifestation of the
3:29same thing? We don't know, but we do
3:30know how to calculate what the thing
3:32will do.
3:33>> So, when it came to torque,
3:36um, I spent years trying to get this,
3:39and other people have asked this
3:40question, too. Give me an intuitive
3:42physical origin for mechanical
3:44advantage.
3:45Because whenever you ask, "Why can I
3:47lift a car
3:49>> Mhm.
3:50>> with a lever? I'm not that strong. I can
3:52stand on one end of a lever and lift an
3:54entire car up. Um you get kind of two
3:57answers. One is, well, it's not that
3:59surprising because force is not
4:00conserved. Like
4:03I still don't have an answer. Or they'd
4:05say, well, you're trading
4:07force for distance. Yes, it's not taking
4:10very much force to lift that car, but
4:12you're having to move a large distance.
4:14And I'm like, how the heck does the car
4:16know what's going to happen? Does the
4:18universe go, hold on, guys, he's going a
4:20long distance, so we don't need the
4:22force to be as high. Are there some
4:24physics police out there that are
4:25telling matter which way to go and what
4:27laws to follow? So,
4:30there was one night, I don't know how I
4:33found this, but I found a paper
4:35titled The Physical Origin of Torque.
4:39And it was a breakdown of exactly where
4:43that mechanical advantage comes from and
4:45why.
4:46And I've made my own models of it, both
4:49physical and digital, to kind of show
4:51this off. I mean, we understand that
4:53that torque comes from the properties of
4:56rotation, that if if if something needs
4:59to move a certain distance, like a
5:02certain, you know, linear distance, but
5:05it's rotating through it, the further
5:06out it is from the center of rotation,
5:08the the the
5:10I guess the smaller that angle is going
5:13to be. You cover like 1 in out here
5:15versus 1 in circling around here.
5:18But,
5:19moment of inertia,
5:21which is how hard it is to rotate
5:23something, depends on that, but also on
5:26something else.
5:28Because the formula for moment of
5:29inertia isn't
5:32mr, mass times radius. Torque is force
5:35times radius.
5:36But inertia,
5:38in the rotational sense, is mr squared.
5:44So, if I've got like a turntable and I
5:46put some weights on it and I use a force
5:49to pull it. Like maybe there's just a
5:50string on a pulley and then some weights
5:53and I let go of it, it's going to start
5:55spinning.
5:56It'll accelerate.
5:58If I move those weights twice as far
6:00from the center,
6:02I need not twice as much torque to get
6:04it to accelerate the same but four times
6:06as much.
6:08Why?
6:10Okay, every answer online and every
6:12answer I got from the people I asked was
6:14well, let's do a derivation of the
6:16formula.
6:17>> Yeah.
6:17>> And they would do it and sure enough
6:20two R's pop out and I'm like don't want
6:22it to pop out. It popped out the second
6:25I touched a crowbar. Like yeah, you're
6:27just describing it with symbols.
6:29>> Exactly.
6:29>> And so to to describe the answer as
6:33given in in this paper, the physical
6:35origin of torque, I kind of need some
6:37like visuals. But the long and short of
6:40it is that not only is there the the
6:42angular advantage, there's also the the
6:46efficiency of force has when it pushes
6:51closer or further from
6:53a pivot point. The efficiency it has at
6:56rotating all of the mass that it's
6:58affecting and that efficiency is not
7:01100% because the speed of sound is
7:03finite.
7:05Because forces don't travel
7:07instantaneously. Objects bend. There are
7:10no perfectly rigid objects.
7:12And if you allow your rod to bend
7:15you realize hold on a second, the
7:17geometry of the lever arms for the force
7:21application point and the load
7:25are different. And it doesn't matter how
7:27much that object bends but when you do
7:29the trigonometry on these angles, what
7:31falls out is
7:35MR squared.
7:36>> And are you satisfied with that as
7:39an explanation?
7:40>> Yes, I am And it's hard
7:44to probably satisfy you because I
7:48haven't yet made this video.
7:50>> Right. Right.
7:51>> And so, I don't have the the like a
7:54honed toolkit for explaining and showing
7:56it.
7:56>> I Yeah, I get it.
7:57>> Um but that's what I'm currently working
7:59on.
7:59>> Well, I've got to say you've I mean,
8:00you've got a talent for that, clearly. I
8:01mean, I think your video on spinning
8:04>> Ah, yeah.
8:05>> is one of the greatest things I've ever
8:06seen. I mean, it I think it's my
8:07favorite video that you've made. It's
8:09just
8:09>> you.
8:09>> because
8:11it's so weird. I mean, it's so weird
8:14that if you like, you know, spin a
8:16bicycle wheel, it will it will stay up.
8:18And it'll And if you if you, you know,
8:19turn it over like that, then you'll
8:21start spinning around on a spin It just
8:23And it's again that feeling of like, you
8:25know, when I watch someone sat on like a
8:26spinny chair
8:28and they spin an object
8:29>> Mhm.
8:30>> and then they go, "Now watch this. When
8:31I turn
8:33when I turn the object, I'm going to
8:34start spinning." And again, it's sort of
8:35like, "How does the universe know? How
8:37does the chair know
8:39>> Yeah.
8:40>> that I've done that?" And it's a it's a
8:42it's a wonderful um
8:43>> So, so which video are you talking
8:44about? The the one whose thumbnail is a
8:46gyroscope?
8:47>> I think it's probably that one. I think
8:48it's called spinning, yeah.
8:49>> another one called Laws and Causes.
8:51>> I'm talking about the first one.
8:53>> Okay. Okay. Yeah, in Laws and Causes, I
8:55double down on that even more, where I'm
8:57like, "If I'm spinning with two weights
8:59in my hand and I pull them in, I spin
9:01faster."
9:03Don't just tell me that it's about the
9:04conservation of angular momentum because
9:06>> Yes.
9:07>> that's just describing what happens.
9:09>> That's not an explanation.
9:10>> Mhm.
9:10>> [clears throat]
9:11>> Now, I don't know if you can ever
9:12totally explain something. That's one of
9:14the problems with explanations, but um
9:17you can draw out some diagrams and
9:18you'll start to notice that when you
9:19pull something in, you're actually
9:22pulling it
9:23um
9:24uh
9:25well, forward or backward, I guess,
9:26depending on which way you're you're
9:28already spinning. And that is what
9:31you're
9:32>> Oh, I see, cuz if you're spinning, then
9:34when you pull inwards, the motion is
9:36actually a kind of forward
9:39Um yes, the path
9:42So if I'm spinning around and I've got
9:44two big weights in my hand and I pull
9:45one in
9:47the path that that weight takes is this
9:49arc. It's a curved path.
9:51It's got this curved path.
9:53And
9:54I'm Let me think.
9:57Um
9:58Oh man, I need to remember this.
10:02The direction
10:04of my force to pull it directly into the
10:06center is actually pulling
10:10like
10:12myself around.
10:14I'm not just pulling the weight in, I'm
10:16pulling myself
10:19I'm accelerating myself.
10:26It's exactly like reaching out to a wall
10:28and pushing off of the wall.
10:30Because I'm able to do that. I'm able to
10:32move myself when I push the wall because
10:33the wall is so much heavier than me. In
10:35fact, it's not just the wall, it's the
10:36entire Earth cuz the wall is like
10:38attached to the Earth probably.
10:41>> [clears throat]
10:41>> I move because my mass is so much
10:43smaller. But when I pull a weight in,
10:46I'm also pushing off of that weight.
10:48It's just that we don't think that you
10:50can push off of something that you're
10:51holding in your own hand. But oops, you
10:53can if you're rotating.
10:55And spinning makes all the difference.
10:57Yeah.
10:58Yeah, and I think I mean
11:00for what it's worth, I think that
11:00explanation
11:03sort of can only go so far. Like I think
11:05that what people end up doing is just
11:07describing something at a at a slightly
11:09lower level, right? And for some people
11:10that's kind of satisfying. I spoke to a
11:12physicist on this podcast
11:14who was very much cuz there's this sort
11:16of debate among scientists. You call I
11:17guess you'd call it like functionalism
11:19about physics that it only tells you
11:21what stuff does. It only describes it.
11:23And then there are people who think no,
11:24it it it sufficiently explains why
11:27stuff's happening. And I was speaking to
11:29somebody who was very suspicious of
11:30functionalism and I said, "Okay, well
11:31suppose that I like blow a trumpet and
11:34that light turned on over there.
11:37And then I realized that if I blow it
11:38louder, the light turns on louder. Uh
11:41the brighter brighter, yeah. And and and
11:43vice versa. And maybe the different
11:44notes are different colors. And I sort
11:46of map this all out and I say, "Okay,
11:48I've I've got this mathematical model
11:49now where I know that if I blow the
11:51trumpet with a C sharp at this volume,
11:53it's going to be a an azure blue at
11:55this, you know, brightness." And I do
11:57it, perfect prediction.
12:00And then I was like, "Do you think that
12:02when someone asks, 'Why is the light
12:03turning on?'" I said, "Oh, because I
12:05blew the trumpet."
12:06And according to my laws of, you know,
12:08trumpet I've explained it. And do you
12:09know what she said? She said, "Yes." She
12:11said, "Yeah, you've explained it."
12:13And I think it's a sort of it's a
12:14mentality thing. Like I look at that and
12:16say, "What you've done is you have
12:17described comprehensively the
12:19relationship between the trumpet and the
12:21light, but you haven't even moved in You
12:22know, it's about prediction. You know
12:24>> Yeah.
12:24How to cause what you want and and you
12:26know what had to precede what happened.
12:28>> Yes.
12:29>> Um
12:30So then I would like to ask that person,
12:32"Well, what if you were then told that
12:35there's a
12:38microphone in the room
12:40that analyzes the sound and then feeds
12:43it into a computer that translates that
12:45into a brightness and a color for the
12:46light bulb. What is that
12:49What's now happened? Has it been
12:51explained in a different way?
12:53>> Yeah.
12:53>> Uh what cuz there's got to be a word for
12:54that cuz that's a very different thing.
12:56>> Exactly. But even then, like I would
12:58then want to say, "Okay, so maybe you
13:00discover that there's a microphone." And
13:02the mic Then you might want to ask,
13:03"Well, you know, why does Why do
13:05vibrations in the air cause an
13:07electrical signal to get sent?" And you
13:09can kind of keep going with this.
13:10>> always keep going and and eventually
13:12you're going to say, "Well, who put the
13:13microphone there?"
13:14>> Yeah, right. Yeah.
13:15>> Who decided that C sharp means azure,
13:18right?
13:19And so explanations never end, and
13:22that's one of the reasons for the
13:25uh illusion of explanatory depth.
13:27>> Yeah.
13:28>> This is a great, uh, psychological
13:30phenomenon. I'm pretty sure you've read
13:31about it.
13:32>> Mhm. I'm not sure I've heard of it, but
13:33>> This is this is the the thing that if
13:35you if you ask people, do you understand
13:37how a helicopter works?
13:38>> Right.
13:39>> They're like, of course I do. And you
13:41go, okay, so how does a helicopter go
13:43from hovering to moving forward?
13:45>> Mhm.
13:46>> And they go, oh, yeah. Well, why does a
13:49helicopter have blades on the tail?
13:52>> That are like perpendicular to the ones
13:54on the top big ones. And they're like,
13:55oh, I don't I guess I don't really know
13:58how a helicopter works. Partly it's that
14:00there's just no end to what you would
14:03need to know to fully understand
14:05something. And so we just have to
14:06default and say, yeah, I do. I get it. I
14:08got it.
14:08>> So it depends on the level that you're
14:11that you sort of that you're looking
14:12for, right? Like if if I
14:14sort of walked into this room and I was
14:17like the architect and I turned to the
14:19to the to the decorator and said, why
14:21are the walls blue?
14:22>> Mhm.
14:23>> They say, oh, because, you know, Johnny
14:25and and the wallpaper department told
14:27us. And so, oh, okay, cool, that that
14:28makes sense. Whereas if it were a
14:29physicist saying, why are the why is the
14:31wall blue?
14:32>> Oh, yeah. Right.
14:33>> And you say, well, because the decorator
14:34said this Yeah, but but but why is it is
14:36it blue? And say, oh, because of the
14:37wavelength that's bouncing Okay, great.
14:39And then you ask the philosopher
14:41says, why is the wall blue? It's like,
14:42oh, because it, you know, there's this
14:43electromagnetic wave that's bouncing off
14:45and
14:46Yeah, but why am I experiencing an
14:48electromagnetic wave at And you can keep
14:49asking why.
14:50>> is what why is blue blue?
14:52>> Yeah.
14:53>> How come when I look at that wall, the
14:55wavelengths don't cause me to taste
14:56hamburgers?
14:57>> Yeah, exactly. Yeah, right. That's a
14:59great way of putting it.
15:00>> question.
15:01>> Exactly. And it's it's it's actually
15:03kind of a continuum. It's not like
15:04you've got three different questions
15:07going on there. I think you've just sort
15:08of got a slightly deeper level of
15:10explanatory depth. So like with the
15:11helicopter, well, the helicopter flies
15:13because the blades rotate. Cool. Or you
15:16could say, why does that? Well, because
15:17of lift. Yeah, but why does lift Why is
15:19air there in the first place? What is
15:21air made out of? What are atoms, you
15:22know?
15:23>> Right.
15:23>> And ultimately, I think that the
15:25scientific method tells you what things
15:27do. That it describes things. To the
15:29extent I mean, Philip Goff was just sat
15:30in the chair that you're in now and and
15:32he's
15:33talks about this a lot about the fact
15:35that ultimately, when you break down
15:36what something is, say the table, it's
15:38made out of wood, the wood's made out of
15:40atoms, the atoms are made out of
15:41electrons and quarks, and you say,
15:43"Well, they they've got mass." You get
15:45to these foundational qualities of the
15:47universe like mass and charge. And you
15:48say, ask a physicist, "What is mass?"
15:50Yeah. "What is charge?" And they'll
15:52define it in terms of what it does.
15:55And there's never [snorts] actually at
15:57the very root, there's never an answer
15:59to like what is
16:02the universe made out of? What is the
16:04the reason why this is happening? And
16:06science is essentially just describing.
16:08So, you're left with this Maybe I'm just
16:09trying to justify, you know, the
16:11existence of of philosophy, which
16:13sometimes you have to do amongst
16:14scientists, but I think there is this
16:16like
16:17ontological gap
16:19at the bottom of of science.
16:21Interestingly, Philip Goff fills that up
16:22with consciousness.
16:23>> Okay. Yeah.
16:24>> So, his consciousness is the thing
16:25itself. And
16:27>> consciousness could be
16:29uh like a third thing. There's there's
16:32matter, and there's consciousness, and
16:35there's
16:36uh What What's What's the What What else
16:39am I thinking of?
16:40>> I don't know, maybe like form.
16:42Um
16:44We could say that it's a foundational
16:45property of the universe. You've sort of
16:46got mass and charge and
16:48>> Yeah.
16:49>> consciousness.
16:50>> Right. Consciousness is just one of
16:51those things.
16:52>> Foundational features, yeah.
16:53>> It doesn't It doesn't come about when
16:54matter's arranged in just the right way.
16:56It It's there and and we just need to
16:59include it into our standard model
17:01somehow.
17:01>> Yeah.
17:02>> Yeah, I mean, I'm sure that might
17:04happen. I I'm still too much of a
17:06reductionist to accept that. I'm like, I
17:08don't know. I feel like I could just I
17:11feel like I could arrange
17:13mechanical
17:15levers and pendulums in just the right
17:17way and it would it would suddenly have
17:18opinions and think and believe it
17:20existed.
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