Angular Motion and Torque

More spinning things! Records, and wheels, and doors, and other fun things. The equations that govern this kind of motion are just like the ones we learned in kinematics, except they have different symbols. Lots of funky Greek letters in this one, folks.
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I like the way that you actually explain what torque is and not just how it is calculated

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i love how he gives us real life examples of usage of torque instead of just telling us that it's a thing that exists that we simply have to accept immediately

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[@Lucky10279]

"Clocks are negative" is how my textbook said to remember that clockwise motion is negative and hence counterclockwise is positive.

[@user-wu2rm3bh4y]

Many people wonder why radians do not appear when we have radians * meters. Here is an attempt at an explanation: Let s denote the length of an arc of a circle whose radius measures r. If the arc subtends an angle measuring β = n°, we can pose a rule of three: 360° _______ 2 • 𝜋 • r n° _______ s Then s = (n° / 360°) • 2 • 𝜋 • r If β = 180° (which means that n = 180), then s = (180° / 360°) • 2 • 𝜋 • r The units "degrees" cancel out and the result is s = (1 / 2) • 2 • 𝜋 • r that is, half of the circumference 2 • 𝜋 • r s = 𝜋 • r If the arc subtends an angle measuring β = θ rad, we can pose a rule of three: 2 • 𝜋 rad _______ 2 • 𝜋 • r θ rad _______ s Then s = (θ rad / 2 • 𝜋 rad) • 2 • 𝜋 • r If β = 𝜋 rad (which means that θ = 𝜋), then s = (𝜋 rad / 2 • 𝜋 rad) • 2 • 𝜋 • r The units "radians" cancel out and the result is s = (1 / 2) • 2 • 𝜋 • r that is, half of the circumference 2 • 𝜋 • r s = 𝜋 • r If we take the formula with the angles measured in radians, we can simplify s = (θ rad / 2 • 𝜋 rad) • 2 • 𝜋 • r s = θ • r where θ denotes the number of radians (it does not have the unit "rad"). θ = β / (1 rad) and θ is a dimensionless variable. However, many consider θ to denote the measure of the angle and for the example believe that θ = 𝜋 rad and radians * meter results in meters. Mathematics and Physics textbooks state that s = θ • r and then θ = s / r It seems that this formula leads to the error of believing that 1 rad = 1 m / m and that the radian is a dimensionless derived unit as it appears in the International System of Units (SI). In the formula s = θ • r the variable θ is a dimensionless variable, it is a number without units, it is the number of radians. When confusing what θ represents in the formula, some mistakes are made in Physics in the units of certain quantities, such as angular speed. My guess is that actually the angular speed ω is not measured in rad / s but in (rad / rad) / s = 1 / s = s^(-1).

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[@heretocomment2337]

Hi @ProfessorDaveExplains I have a few questions about torque that I don't know if you already covered in this video, because to be honest, I didn't watch it all, but you are the only one on youtube making videos on this topic that replies. Here are my questions: 1. What absolutely decides whether rotation is clockwise and anti-clockwise? In a 3D spinning item, such as a bicycle wheel or even a ferris wheel like you said, has 2 sides. On one side, no matter how it spins, it will be clockwise, and the same wheel will appear to be anti-clockwise when viewed from the other side. 2. How does torque have a direction in or out of the page? I know the right hand rule RHR, but it doesn't explain anything. Taking the bicycle wheel or the ferris wheel as an example again, think about the axle: when looking at the wheel from the side so all you see is a thin rod, the axle sticks out on both the left and right, but when applying the RHR, and you pick a side, any side, your thumb will invariably end up pointing at either one of the left or the right... it's just a matter of which side you choose. Further, even if the sides don't matter for points 1 and 2 because the mathematical signs will reverse which ultimately end up cancelling, what does it mean when people say torque has a direction in or out of the page? If a spoke in the bicycle rotates as the wheel spins, it spins either clock or anti clockwise depending on how you look at it. The force applied to it is perpendicular to the spoke on the same 2D plane as that of the flat surface of the wheel. However, if you used the right hand rule, your thumb will point in either direction of the axle that sicks out. But that's not where the force is, you are not pushing on the wheel from the side (remember we are looking at the wheel from the side so we only see the thin profile of the wheel tread and no spokes). What is there? How can you say that "torque comes out or into the page/plane" when torque is the force you applied to it (eg to the spoke) to make it turn? Thank you in advance and sorry for the long question.

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Great explanation. Thank you so much!

[@user-wu2rm3bh4y]

My guess is that actually the angular speed ω is not measured in rad / s but in (rad / rad) / s = 1 / s. If we say that the measure β of the angle is θ radians, we mean β = θ rad, and θ is the number of radians (it does not have the unit "rad"). For emphasis we can say that θ is measured in rad / rad, since θ = β / (1 rad) and θ is a dimensionless variable. When we use mathematical formulas to obtain formulas in Physics, we have to know what the variables represent. What I consider a mistake, is present in the literature, it is not only in this video. Therefore, I will leave another comment with the detailed information to be examined.

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But what did Archimedes say next

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[@heartofblackonyx]

there is a right hand rule for keeping track of positive or negative rotation that is much more robust and systematic than what he describes.

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I love your work so much, but if you can extend your videos to go a bit slow while explaining, thanks for your patience

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try setting it to 0.75 speed if you need more time

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Thak you!! Great video!! I was really happy to find info about inbetween perpendicular applied force and parallel applied force for torque

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When the video start I was sleepy, but as you arrive at Torque I stood up. KEA LEBOGA.

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[@kostasbaganas3681]

FYI: π is not pronounced as 'pie' in Greek, but more like a 'pe' instead. The same holds for the wave function in Quantum mechanics ie. 'pse' instead of 'psie'. Also, torque τ is read as 'taph' (or 'taf'') instead of 'tao' ('taou').

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im not interested in learning pronunciation

[@carultch]

In English, we have to shift the vowel when we say the letter π. Otherwise it would sound identical to the Latin letter p. It is a consequence of the great vowel shift in the history of English. Other languages that use the Latin alphabet, call the letter "pay", instead of "pea", and can retain the original Greek name of π, and still tell them apart.

[@KalpPatel]

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That transition at the end tho lol :)

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Thank you made me understand this,but sometimes are too fast when explain other topics like momentum

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👍

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Sir please also give us some more questions which are in HOTS so that we can know how to apply those concepts ! Thank you sir

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3.3 mtr

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[@bibilihills5062]

In the last question why net torque must be zero?

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I like the "TAU" you pronounce😃🤪

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Ok so what does the 9.8 represent

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Gravitational acceleration

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Sir, please make videos on moment of inertia

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check out my tutorial on newton's first law of motion!

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I think there is a problem with the significant figures

[@moontonaccount9489]

Hey, would't the lever that will move the earth be faster than the speed of light since it will transfer force faster than light? So it will mean that something can travel faster than light?

[@shaherfurany3926]

in your example the rod was horizontally placed , what if the rod was vertically placed ? then the force ( torque) will be perpendicular to the rod and consequently sine turns into cosine ??

[@anaghaanagri2159]

It's always sine theta because theta is the angle between the force (torque) and the plane of rotating object (in other words , the displacement vector )and not the angle between the force with the horizontal. Torque is force times the perpendicular distance between the force and plane of rotating object.

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2rsinc/t is it correct angular displacement c is angel

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[@suzumii2998]

sir the unit of torque is NM that is joules. so work, energy and torque are the same quantities?

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Profesor Dave, do you have any videos on rolling without slipping motion?

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[@fredmahony5714]

I guess we will never know what else Archimedes said.

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