Welcome to the presentation

on torque. So, if you watched the

presentation on the center of mass, which you should have, you

might have gotten a little bit of a glancing view

of what torque is. And now we’ll do some

more in detail. So in general, from the center

of mass video, we learned, if this is a ruler and this is the

ruler’s center of mass. And if I were to apply force at

the center of mass, I would accelerate the whole ruler in

the direction of the force. If I have the force applying at

the center of mass there, the whole ruler would accelerate

in that direction. And we’d figure it out by

taking the force we’re applying to it and dividing

by the mass of the ruler. And in that center of mass

video, I imply– well, what happens if the force

is applied here? Away from the center of mass? Well, in this situation, the

object, assuming it’s a free floating object on the Space

Shuttle or something, it will rotate around the

center of mass. And that’s also true, if we

didn’t use the center of mass, but instead we fixed

the point. Let’s say we had

another ruler. Although it has less height

than the previous one. Instead of worrying about its

center of mass, let’s say that it’s just fixed at

a point here. Let’s say it’s fixed here. So if this could be the hand

of a clock, and it’s nailed down to the back of the

clock right there. So if we were trying to rotate

it, it would always rotate around this point. And the same thing

would happen. If I were to apply a force at

this point, maybe I could break the nail off the back of

the clock, or something, but I won’t rotate this needle or

this ruler, or whatever you want to call it. But if I would apply a force

here, I would rotate the ruler around the pivot point. And this force that’s applied a

distance away from the pivot point, or we could say from the

axis of rotation, or the center of mass. That’s called torque. And torque, the letter for

torque is this Greek, I think that’s tau, it’s a curvy T. And torque is defined as

force times distance. And what force and what

distance is it? It’s the force that’s

perpendicular to the object. I guess you could say to

the distance vector. If this is the distance vector–

let me do it in a different color. If this is the distance vector,

the component of the force is perpendicular to

this distance vector. And this is torque. And so what are its units? Well, force is newtons, and

distance is meters, so this is newton meters. And you’re saying, hey Sal,

newtons times meters, force times distance, that looks

an awful lot like work. And it’s very important to

realize that this isn’t work, and that’s why we won’t

call this joules. Because in work, what

are we doing? We are translating an object. If this is an object, and I’m

applying a force, I’m taking the force over the distance

in the same direction as the force. Here the distance and

the force are parallel to each other. You could say the distance

vector and the force vector are in the same direction. Of course, that’s

translational. The whole object

is just moving. It’s not rotating or anything. In the situation of torque,

let me switch colors. The distance vector, this is the

distance from the fulcrum or the pivot point of the center

of mass, to where I’m applying the force. This distance vector is

perpendicular to the force that’s being applied. So torque and work are

fundamentally two different things, even though their

units are the same. And this is a little

bit of notational. This distance is often called

the moment arm distance. And I don’t know where

that came from. Maybe one of you all can write

me a message saying where it did come from. And often in some of your

physics classes they’ll often call torque as a moment. But we’ll deal with

the term torque. And that’s more fun, because

eventually we can understand concepts like torque

horsepower in cars. So let’s do a little bit of

math, hopefully I’ve given you a little bit of intuition. So let’s say I had this ruler. And let’s say that this is its

pivot point right here. So it would rotate around

that point. It’s nailed to the wall

or something. And let’s say that I apply a

force– Let’s say the moment arm distance. So let’s say this distance,

let me do it in different color. Let’s say that this distance

right here is 10 meters. And I were to apply a force of 5

newtons perpendicular to the distance vector, or to dimension

of the moment arm, you could view it either way. So torque is pretty easy

in this situation. Torque is going to be equal to

the force, 5 newtons, times the distance, 10. So it would be 50

newton meters. And you’re probably saying,

well, Sal, how do I know if this torque is going to be

positive or negative? And this is where there’s just a

general arbitrary convention in physics. And it’s good to know. If you’re rotating clockwise

torque is negative. Let me go the other way. If you were rotating

counterclockwise, like we were in this example, rotating

counterclockwise, the opposite direction of which a clock

would move in. Torque is positive. And if you rotate clockwise

the other way, torque is negative. So clockwise is negative. And I’m not going to go into

the whole cross product and the linear algebra of torque

right now, because I think that’s a little bit

beyond the scope. But we’ll do that

once we do more mathematically intensive physics. But, so, good enough. There’s a torque of

50 newton meters. And that’s all of the torque

that is acting on this object . So it’s going to rotate

in this direction. And we don’t have the tools yet

to figure out how quickly it will rotate. But we know it will rotate. And that’s vaguely useful. But what if I said that the

object is not rotating? And that I have another

force acting here? And let’s say that that force

is– I don’t know, let me make up something, that’s 5

meters to the left of the pivot point. If I were tell you that this

object does not rotate. So if I tell you that the object

is not rotating, that means the net torque on this

ruler must be 0, because it’s not– its rate of change of

rotation is not changing. I should be a little exact. If I’m applying some force here,

and still not rotating, then we know that the net torque

on this object is 0. So what is the force

being applied here? Well, what is the net torque? Well, it’s this torque, which

we already figured out. It’s going in the clockwise

direction. So it’s 5– Let me do it

in a brighter color. 5 times 10. And then the net torque. The sum of all the torques

have to be equal to 0. So what’s this torque? So let’s call this f. This is the force. So, plus– Well, this force is

acting in what direction? Clockwise or counterclockwise? Well, it’s acting in the

clockwise direction. This force wants to make the

ruler rotate this way. So this is actually going

to be a negative torque. So let’s say, put a negative

number here times f, times its moment arm distance, times

5, and all of this has to equal 0. The net torque is 0, because the

object’s rate of change of rotation isn’t changing, or if

it started off not rotating, it’s still not rotating. So here we get 50 minus

5 f is equal to 0. That’s 50 is equal to 5 f. f is equal to 10. If we follow the units all the

way through, we would get that f is equal to 10 newtons. So that’s interesting. I applied double the force

at half the distance. And it offsetted half the force

at twice the distance. And that should all connect, or

start to connect, with what we talked about with mechanical

advantage. You could view it

the other way. Let’s say these are people

applying these forces. Say this guy over here is

applying 10 newtons. He’s much stronger. He’s twice as strong as

this guy over here. But because this guy is twice

as far away from the pivot point, he balances

the other guy. So you can kind of view it

as this guy having some mechanical advantage or having

a mechanical advantage of 2. And watch the mechanical

advantage videos if that confuses you a little bit. But this is where to

torque is useful. Because if an object’s rate of

rotation is not changing, you know that the net torque

on that object is 0. And you can solve for the

forces or the distances. I’m about to run out of

time, so I will see you in the next video.

why is that, if we push a door from the corner most side we have to apply less force in order to rotate it by an angle ?. I know that the torque will be more but it is way to mathematical torque = force x length of the arm . I don't want to know it mathematically but physically .

Torque sounds like Twerk idek

it's just like Equilibrium

Think about the distance your hand his moving versus the distance moved by the center of the door. At the handle, your hand moves about twice as much as the door, but near the hinge, your hand hardly moves at all, but the door moves a lot.

Excellent video, thanks for the closed caption.

Saya suka

"You know then that the net twerk is zero"

That was literally what I personally heard

Torque? I think its TWERKK!!! LOL

what is the difference between torque(F *D)and moment (NAI )? phesically

These videos are amazingly helpful while studying! A good example to use in future would be a see-saw, and I suggest that small points you mutter to be made clearer, like all the torques equal 0, I had to re-watch the video to find that. But otherwise fantastic job thank you so much!!

You're voice is so soothing at 12:30am 🙂

Miley's favorite Physics topic.

>Desperately look for videos explaining the topics of interest.

>See Khan Academy video

>smile on my face

I swear he moves so dam slow . I have to smash my arrow button so I can keep the problem going.

i like how this is a physics video yet 75% of the comments below are completely irrelevant lmao

5:38 lol it's a dick

i love khan academy

So what does it mean if a car has 604 lb.-ft. of torque at 3800 rpm ?

and is it better to measure a cars power in horse power or torque?

this was no helpful i have a problem getting to the point you are trying to make

Is this the same as a moment?

Twurk It Out Sal!!XD

Why some videos are private? What so special?

Thanks you soooo much…..now i've understood why my uncle was able to open up the car tyre's screw with a longer pipe…….. when i had been kicking so hard with a shorter one but still wouldn't open!!!!!!!!!!

wrost

Sal, I love physics but i am just can't understand it as fast as math

Great explanation Bro! Thank u

As usual I love science, I love Sal. Outstanding explanation!

Just a question: if the object is in a space shuttle, how does the mass at the centre act as a pivot? Or is it just a misconception?

"Moment arm", I think "arm" is from the terminology regarding levers ("lever arm"). Moment is a combination of a physical quantity and a distance ("moment of force" is synonymous with "torque").

I have no idea why it should take 9 minutes to explain how to multiply 2 numbers together. It didnt even go into torque at angles! Usual Khan Academy videos. Great lesson, but at the expense of wasted time.

After about the 12th video of Khan Academy, I hope everyone realizes to put this guy on speed X 2. Settings-speed-2.

I like to visit you one day and thank you for everything I learned and learning from you.Hus.Australia

Introduction to Torque gets over half a million views.. talk about an outstanding job!

Your way of teaching is amazing, love it

could not have explained better!!!😍😍😍

Great explanation !

😊😊😊😊😊😊😊

great explaination 😀 thank you

thank you so much

Isnt torque f x d instead of f.d

Hey look it 's a cross product.

woah i get itttttttttttt!!!!!!!!!!!!!

So basically when we say a car has 500Nm of torque, we basically say that the engine turns faster compared to a car with 100Nm of torque >>??

Thank jegus for this channel. If this didn't exist, I would've failed my physics final.

Good basic explanation. Wish i could find videos that actually match the rigor of my physics class :/

if you push an object at a point other than centre of mass it will start rotating right? so what if im in space and someone pushes my legs and as I start rotating, i change my position thus my cm?

Altyazili olanlar cok daha kullanisliydi acikcasi

Nobody Can understand by any vedio because of "Internet"

I think torque is cross product not dot!!!

thank you for your explanations.now i got one doubt that whenever while finding the torque why should we take the force which is perpendicular to the axis of rotation? is there any reason ? explain me if someone knows….

I love you…so much

torque=r×f not f•d

Physicist use the term "torque" while engineers refer to the term "moment." So instead of saying lever arm, they carried that aspect over creating "moment arm."

Yabançı Umut Öncül

it helped a lot

what is the difference between torque and moment sir?

How can i download this

thxx bro u were helpful😆😆

thxx bro u were helpful😆😆

Torque to me.

Thumbs up ! 🙂

what is the name of the program your writing on?

You've taught me more than my construction teacher did in three 30 minute lectures

this was helpful thank you

those explanations were great though nice work sal

My new PHYSICS SOLVING APP.More then 150+ formulas,Solves for any variable you want,Covers up all physics.download now.https://play.google.com/store/apps/details?id=com.physics.lenovo.myapplication

One thing I hate is when you say ' i dont know' in most of your video

It's not just about force and displacement being perpendicular to each other… it's the dot product

How do we know if it is clockwise or counterclockwise if it does not specify?

very helpful! thanks a lot

where is angular momentum

be my physics teacher plZzzzzzzzzzz

Thank you for the explanation !!

https://www.youtube.com/watch?v=xxPWshcQy-8

U forgot weight of ruler

Good explanation but not good language pls specify the frame of reference ur talking and write equations in hard-core vector form

Superb!

why is clockwise torque regarded as negative

Love this video. Helped me a lot

Incredible what I can learn in 9 minutes that a trained adult cannot explain in 50. Hmph

"What twerk is.." 😂😂

1m shows that lots of people had a bad physics teacher

When even your boy Khan can't save you physics grade

👌

why torque = force * distance from the point of rotation

i hope you have the guts to remake these videos on a decent resolution one day

noob delete cs go

I have a doubt.can anyone pls clear it?

Are moment of force and torque the same?

please , I have been extremely keen to know , in the equation where: driving force*speed = power , when the speed is zero , like if an engine is going to move a car that is at rest , what exactly goes on , thanks

is torque the same as work. it is a vector but has the same dimensional formula

Difference between torque and moment??????????????😶

The equation of torque is tau=r x F, but the formula that you give me is tau=F x d, which is equal to the -(r x F).

Me: Realizing that I am watching this on youtube and not getting any arbitrary energy points…

concept in useful

Should be cross product though not dot product bruh