Demonstrating Rotational Inertia (or Moment of Inertia)

[@acampinglamp]

Probably the best moment of inertia explanation I’ve seen and I finally understand it. So grateful for people like you

[@FlippingPhysics]

Thanks for the compliment!

[@learningscienceisfun]

Nicely done! Great demo too!

[@Ami_S]

This definitely one of the best explanations out there. I checked out several videos and they just gave the formula and told that moment of inertia is the rotational analogue of mass. This didn't make complete sense to me. As F=ma (linear 2law) , if F is constant, if mass increases the acceleration decreases. Similarly when torque was constant, if mass increased angular acceleration decreased which suggests the 'm' part in rotational inertia. Then you proved how the 'r' part comes into the picture. As the radius of the mass increased, given the torque constant, the angular acceleration decreased. This shows that m and r together form the 'm' term in F=ma as when the mass and radius of the objects increases, it resists rotation. Hence T=Ia as if torque is contant, m and radius are the determiners of the angular acceleration. We know that torque is proportional to fishy thing and the proportionality constant becomes mr^2 (I had a confusion as to why r^2 and not r but then when I calculated the dimensions using t proportional to a, t=Ia , I=T/a and the units was kgm^2). This clarity I got only after watching your video. Thanks alot. Do let me know If I have gone wrong anywhere with the understanding. I am definitely recommending you to my friends.

[@pedro_pinheiro]

Great content! You're helping me teach rigid body dynamics to engineering students for free. Thanks! I'll recommend your channel as much as I can.

[@FlippingPhysics]

Thanks for all the recommendations!

[@jlpsinde]

Obrigado!

[@gracygohil6791]

The bestest explanation ever. Thank you for this .

[@FlippingPhysics]

You're very welcome!

[@prathikkannan3324]

You are such a good teacher. You make physics so intuitive. I hope to watch more of your videos to gain a better understanding for how beautiful physics really is.

[@manikkpr2375]

This is best channel for physics! Which teaches us physics in physics way! Not just some chunky formulas

[@FlippingPhysics]

Glad you think so!

[@noor37083]

You seem to put a lot of effort in those videos, thank you so much, I wish my teacher’s explanation was like that

[@talifishman618]

you're seriously the only thing getting me through university thanks man

[@ChaineYTXF]

Read and work all of Goldstein's Classical Mechanics book. 1 month or two of serious work and you'll be surprised at how good you are.

[@sanjaySingh-ck6kd]

This is the Best Moment of Inertia explanation I have heard / read. Flipping Physics is the best. Great content along with superb explanations. Thank you.

[@FlippingPhysics]

Glad it was helpful!

[@frijolex2509]

Love your videos. They really help in tying loose ends when learning these topics. The visualizations really seal the deal.

[@KBAZ100]

"Where are you taking this THING?" Great STAR WARS reference! You are awesome Mr. P! :)

[@FlippingPhysics]

Thank you! It was actually someone else's idea to add that in there, but I thought it was hilarious, so I added it. I was afraid it might be too subtle. Glad you noticed!

[@Marcosss-7-years-ago]

4:47 middle one doesnt blink, i thought he was dead😳

[@rithvikyagnamurthy6560]

tbf I feel like Bobby in every Physics class

[@Sun.s.Lantern]

😭

[@Jawadalishah69]

Wow😭 can’t believe how good this video is

[@FlippingPhysics]

Thanks!

[@eliyahomar]

you are unbelievable, thank you so much for doing your best to make this simple by running experiments

[@FlippingPhysics]

Glad to help! (Experiments make it easier to understand. 😬)

[@universebeyond4827]

Just searched on youtube 'best video on moment of inertia' & it took me here...to a video from my own subscriptions😃 Thanks again #FP

[@FlippingPhysics]

You are very welcome

[@davidliu3463]

This is the second time I watched yr video. The first time was explannation of action reaction force misconception, that was really good and I recommended that to a lot of friends. This video is also well made, its especially impressive that you tend to cover misconceptions and questions that students might come up with Thx so much

[@dominiccirineo1587]

Absolutely beautiful lesson, magnificent work!

[@FlippingPhysics]

Thank you!!

[@adleneboulebtateche156]

Thank you for the explanation, the excellent acting performance and the beautiful editing.

[@FlippingPhysics]

Thanks for the love!

[@Carlosk12]

Yess just in time!! We just started our rotational motion unit last week and i was getting confused

[@FlippingPhysics]

You are welcome!

[@mohammedalafandy7551]

Great demonstration

[@deepakulkarni5116]

the best video on RM ever! thanks a lot

[@nz7025]

I think, the video I was searching for, is this! Great job 💓💓💓

[@eljison]

Excellent demo and exlanation! May I suggest one correction to the notation? Near the @5:00 mark, the equation displayed is notationally incorrect. We can write the torque vector equal to the vector product of the radial vector and the force vector ("r cross F"), but when we write the equation in scalar form, the magnitude of the torque is equal to the magnitude of the radial vector times the magnitude of the force vector times the sine of the angle between the vectors when they are tail to tail, we need to drop the "arrows" on the symbols (or put the double- or single- bars around them depending on which notation you prefer for the "norm" or magnitude of a vector). Vectors cannot be stuck together without a "dot" or "cross" because that is an undefined operation, unlike scalar algebra where "a cross b" = "a dot b" = ab. I apologize for not being able to format mathematical operations in the comments.

[@FlippingPhysics]

Thanks. I am aware of this issue and, if KZbin allowed uploading of replacement videos, I would upload a replacement for this with that correct. Unfortunately, KZbin does not allow that. It's a bummer. Wish I were perfect, or at least able to fix my mistakes.

[@jaijeffcom]

Okay, seriously cool. I study statistics, which summarizes the dispersion of a probability distribution as its variance. The definition of variance equates to moment of inertia. Statistics therefore borrows the physics term, describing variance as the second central moment. With this lucid video, I now better understand variance.

[@FlippingPhysics]

I had never heard this before. Wonderful to learn. Thanks!

[@ChaineYTXF]

1:41 torque is a pseudo-vector😉 3:49 : vector *r* next to vector *F* with no symbol between. That notation exists but in a different context: *r* *F* is the geometric product of both vectors, not its cross product) (I put vectors in bold letters, easier here)? Don't you rather mean the norm of each times sin(θ) (where θ is the angle between *r* and *F* ), like so: | *τ* | = | *r* | × | *F* | ×sin( *r* , *F* ) ? (note for readers: here × denotes usual multiplication, whereas in *r* × *F* it denotes the cross product. Non anglo-sphere students might use ∧ for cross product) Very nice video

[@FlippingPhysics]

I do. Wish KZbin would allow me to make subtle changes like that...

[@eljison]

Why are you calling torque a pseudovector? I've never heard it referred to that in a physics context, unlike pseudo-forces. At this level, students have a hard enough time grasping that centrifugal force is a pseudoforce. Also, this is the first time I've come across the geometric product, though I vaguely recall coming across an inner vs. outer product. As this video is intended for introductory physics students, most of those subtleties are lost on the student so not worth mentioning. I usually say that operation is "undefined", which is not quite true but gets them to stop writing vector multiplication without the dot or cross symbol in some cases. When you only teach introductory courses you lose some of the more advanced mathematics, but it really does not need to come up in this context.

[@alejrandom6592]

omg I can't believe I didn't know about this channel i luv it

[@johnwilson1754]

Cool demonstration. Thank you.

[@alex.petrunak]

who's watching this because of online learning?

[@Raj-mu9kp]

I like the way of presentation.

[@behlolyaseen786]

your are teaching us as well as yourself excellent presentation

[@zainabhussain3887]

The middle one gonna catch a fly. Ask him to close his mouth🤣😂

[@undergroundeieiz5508]

Super helpful experiment

[@syedsaleem8631]

Very good explanation

[@z1zn]

this is awesome ! thank you ! i really like your method .. you make it easy to understand !

[@FlippingPhysics]

Thanks.

[@allswell5688]

Thank you Soo much ❤️💕 From North East India 😊

[@mallondan]

Superb. The best ever lesson I've watched.

[@FlippingPhysics]

Wonderful praise. Thank you!

[@andrewjustin256]

6:08 Why is the moment of inertia of this system same as of the previous system? Shouldn't the Rotational inertias be added? It feels like you subtracted 100g from 200g ending up with a hundred gram. Is that what you did but the question is why? Moment of inertia is not a vector

[@abhishekbishnoitechnical439]

I just love this presentation.

[@kennethliu3268]

Dude that was a really good demonstration

[@FlippingPhysics]

Thanks!

[@shabnamkhatoon4980]

Wow a practical explanation gazab sir gazab 😮🙃.seeing it in 2020

[@angadsingh612]

Great experience sir osm.....

[@Szhihihihihihi]

Thank you !

[@samanthaknepp3096]

Great video!

[@charlieredeemed]

The way the Queen on the right got the momentum just by flexing one CheeK; she found the secret to rotational-intertia and perpetual-motion🤓👍🏼👏🏼

[@Sun.s.Lantern]

SUBSCRIBED!!! BRILLIANT AND FUN! 😂

[@Ivy-qm5bq]

this is brilliant

[@iridianramos9083]

Hi! I have a question. I'm doing an experiment based on this showing how the moment of inertia changes based on different distributions of mass. This relationship can be demonstrated by shortening the string length of a simple pendulum and measuring the velocity at the bottom of its swing for each string length. However, I'm confused on why my experimental velocities are all different from each other. I was told this would work by my physics teacher, but I'm confused. If the height to which I'm raising the pendulum doesn't change for each string length and therefore, neither does the potential energy then neither should the kinetic energy for each new string length. But all of my velocities are different. I know the angular velocity should be different but I'm finding the time taken to swing at the bottom of the pendulum (then used to find the velocity and then the angular velocity) changes when it shouldn't. Essentially, experimentally the velocity at the bottom of its swing changes between different string lengths indicating changes in angular velocities but theoretically, the velocity shouldn't change and only the angular velocity should. What is the theory behind these theoretical and experimental differences?

[@medidiotMBBS]

Awesome lecture and thank you for your efforts

[@siddharthannandhakumar6187]

What if we eliminate gravity when the centre of mass of decentralised?

[@Fencer1128]

Incredible help, thank you

[@FlippingPhysics]

And I thank you for the lovely comment.

[@Magnus..]

thats so much effort

[@nz7025]

And yeah, you got a new subscriber 😄

[@kaviisworld]

if center of miss is closer one in right side and object of center mass is farther left side then which will spin longer and faster ????????

[@AtAGlimpse_UB]

DOUBT: In demonstration #3, Does the system on the left have more angular acc?

[@TheCozyBoy-c6d]

great video

[@udaysingh5167]

HI SIR! I AM FROM INDIA.❤️ I LIKE YOUR EXPLAINATION.

[@FlippingPhysics]

Glad you enjoy it!

[@nave2n]

I gues love seeing these videos. Kepp going guy or guys lol

[@ThePartyzanin]

Well, that was a nice lesson!

[@aryan7767]

Hi. if I were to investigate the effect of a particular variable on rotational inertia where I can get a graphable equation, which variable would you recommend? Great video btw

[@impactodelsurenterprise2440]

Don't you need to add in the mass of the shaft too for the total moment of inertia in order to calculate the required torque to turn the whole thing?

[@FlippingPhysics]

Yes. See: www.flippingphysics.com/thin-rod-rotational-inertia.html

[@impactodelsurenterprise2440]

@@FlippingPhysics Thanks! Can you make a video of how to calculate inertia for a pumpjack?

[@abhishekbishnoitechnical439]

I watch this video six times. and every time's learn something new. so increase the watching frequency thet increase your knowledge and reduce fear about physic just like increase torque due to increasing the acceleration

[@saavestro2154]

awesome video, also funny

[@FlippingPhysics]

Thanks!

[@Hanuman120]

I enjoyed the video. However, I was expecting you to get to the fact that the acceleration of the 2 mass system is less than that of the single mass, just like with an Atwood Machine. We now have an additional 200 g of inertia, all with the same net force. Since more of the potential energy has to go to translational kinetic, a bit less goes to rotational. I can understand not wanting to go into this detail in your video. I know that you said "roughly" at the end, so I figure this detail is outside of the scope of your video. I probably would have mentioned this in my classroom, though. Thanks for making these!

[@FlippingPhysics]

Making these videos is always an act of restraint. Think of all the things that are _not_ in this video: - Free body diagrams. - The relationship between velocity of the hanging mass and the tangential velocity of the exterior of the pulley. - Friction in the axle causing torque. - Conservation of mechanical energy. This video is meant to be a basic introduction to rotational inertia. I felt it necessary to have one example with two torques because students often forget it is the _net_ torque in the rotational form of Newton's second law. Someday I hope to make a video which quantifies the "roughly" word you pointed out I used at the end. Trust me, quantifying that will take a full video of its own. You are absolutely welcome for the videos!!!

[@jlpsinde]

Amazing

[@casperjowo]

Ada yg bisa nyimpulkan gak?

[@gensyed]

May I ask why speed does not affect rotational inertia?

[@FlippingPhysics]

Does speed affect the mass of an object?

[@gensyed]

@@FlippingPhysics by its definition , mass always remains constant, unless it ownself is the creator of speed. In a gravitized environment, a rotating body is counter directional-one facing gravity and the other against it. Do this condition affect its momentum or inertia? Consider an object in an elevator going up and down.

[@carultch]

@@gensyed Gravity doesn't affect moment of inertia. It will apply an alternating torque to an object, if not rotating around its center of mass, but it doesn't make the ratio between net torque and angular acceleration any different.

[@phenomenalphysics3548]

But why is it R squared and not R cubed or just R

[@FlippingPhysics]

I derive rotational inertia (or moment of inertia) here: www.flippingphysics.com/moment-of-inertia.html

[@phenomenalphysics3548]

@@FlippingPhysics thak you so much you saved my life! You're doing a great job. You have no idea how much its helping me! Ps: I have a really bad physics teacher at school

[@chupbey7814]

@@phenomenalphysics3548 your name is phenomenal physics and you don't ask questions from other physicists ... 😏Absurd

[@WrongDescription]

Thaks a lot

[@FlippingPhysics]

you are welcome

[@24.msrikaran60]

I would be having better fun if i had you as my physics teacher

[@MolotovWithLux]

From mass of Inertia to #rotationalInertia Like the floating air balloon without helium

[@ameerhamza4816]

Why your students look exactly as you!!!

[@FlippingPhysics]

Perhaps this is why? flippingphysics.com/making-a-video.html

[@subikksha4941]

@@FlippingPhysics My god! I saw the video. May God bless you! So much hard work for us, saying thank you is an understatement sir!

[@FlippingPhysics]

@@subikksha4941 Thank you for your kind words!

[@subikksha4941]

@@FlippingPhysics I'm just stating the truth sir :)

[@chupbey7814]

@@subikksha4941 Indian students so kind ! 😁

[@asyayekta7095]

I don't know Good English but I want to watch the videos.pelase turkish subtitles.I love physics.I am Turkish

[@mikes.4863]

There has to be an easier way to explain this. Has to be. I just watched this other video that stated "the diver who is curled up will tend to stay spinning, whereas the diver who is stretched out will be less likely to spin". That makes sense. Buy then they said "the diver curled up has a low moment of inertia". WHAT???? How could he have a "low" moment of inertia when he is MORE likely to keep spinning---to "remain unchaged". Its so ridiculous.

[@ProNoobAgarCOC]

If only students were as smart as your students haha

[@jonathana9236]

I used to be the middle guy.

[@oijosh6286]

Billy is Nardwuar in disguise 🤭

[@meherbabagodinhumanform9414]

🥰🥰💗💗😍😍

[@ajgameshacker7165]

Sir please reply.....

[@nasirkhalid6770]

Don't worry he always reply.

[@robertiii796]

Nasir Khalid rip

[@chupbey7814]

@@robertiii796 lol

[@ajgameshacker7165]

1st view and 1 comment

[@ajgameshacker7165]

Sir i am your biggest fan from india ... And wating for you each video And i am your suscriber from 50 Sir may you provide your contact no. So it help me a lot ... Thank you

[@FlippingPhysics]

AJ Games Hacker. Know I appreciate your support. Also understand that I cannot give you my contact information. There are a large number of people who want to contact me and I just cannot communicated with all of them. I have to protect my time to be able to make videos to help you learn. I hope that makes sense. -mr.p

[@rounitkamal2832]

Great video