Measuring Mass Moment of Inertia

Measuring Mass Moment of Inertia - Brain Waves

Рет қаралды 21,828

7 жыл бұрын

It's relatively easy to measure mass moment of inertia of an object using a bifilar pendulum. Here's a description along with a derivation of the governing equation and an experiment to show how it all works.

Пікірлер: 53

@tomasenrique 7 ай бұрын

English is not my first language, but boy your accent it PERFECT!!! I don't need any subs for these videos!

@gdogvibes1 6 жыл бұрын

Really enjoy your teaching style. Very informative but not dry and genuinely enjoyable to watch, thanks!

@tommcqueary7831 6 жыл бұрын

Great Explanation This information will help me model my quadcopter which I am designing and building including the control board. This kind of information was lacking in my college control systems course (EE curriculum). It seems the most difficult part of controlling a system is to get an accurate model of the system so this information along with modeling the motor torque will solve major pieces of the puzzle. Thanks for a great effort. Only minor complaint is it seems you may need to replace one of your felt tip markers soon.

@gokulkrishna2621 6 жыл бұрын

thanks a lot professor.... you saved my day...

@hassanmualla3693 6 жыл бұрын

Wow! Really helpful!

@cakecakeish 7 жыл бұрын

Excellent video! Explained so well. Where did you get the equation to work out the mass moment of inertia from? Which textbooks are you using? Thanks!

@alieltair5418 4 жыл бұрын

Hello, I was using this formula in my experiment to test the parallel axis theorem, however, I quickly realized that it only works when the rotational axis is at the center of mass, is there any iteration of the formula that considers having the rotational axis away from the center of mass? Help appreciated!

@yankeekilo 3 жыл бұрын

Thank You sir!

@nickgodden1980 7 жыл бұрын

Always great seeing an experiment to prove the maths....you'll have to apply for funding for a more comprehensive lab 😀 Thank you.

@feelingk 2 жыл бұрын

Thanks for very interesting video. I would like to apply this method to mesuring the mass moment of inertia (MMoI) of my robot. However, I have following questions: i) MMoI depends on mass (of course mass distribution) and geometry of the object. For a defined object, can be considered as a constant. This results to b^2 T^2 /L = const. Is it true? ii) If i) is not true, then it means that MMoI depends on b, distance from the CoG to the point where you hold the cable. So, where is that point for obtaining a good value of MMoI?

@taurinenrgy 7 жыл бұрын

That was amazing! so would this method work on other more complex objects as well, like your skate board or a tree branch?

@purdueMET 7 жыл бұрын

In theory, it should work on just about anything. The Air Force uses this method to find the MOI of underwing stores like fuel tanks and missiles.

@taurinenrgy 7 жыл бұрын

Thanks, I used this method for my physics lab along with using a turn table to find the moment of inertia and I got close to the same result both ways.

@nishantmishra5604 11 ай бұрын

@@purdueMET I was trying to find the MOI of my Styrofoam glider, but it is almost impossible to balance the aircraft

@user-yj8ji1wm3i 3 жыл бұрын

Thanks for the tutorial, and just a small question. What if the CG is not at the center of D. Does the derived equation still works or any modification suggested. Great thanks in advance

@BobbyBlue117 3 жыл бұрын

The derivation requires that both tensions be the same which will place the CG somewhere between the two strings and along the line connecting the two strings as well.

@koolkataustin2961 4 жыл бұрын

how did you get bθ in the right angle triangle?

@koolkataustin2961 4 жыл бұрын

what is bθ supposed to represent

@koolkataustin2961 4 жыл бұрын

Also, if in the equation I=(Mgb^2t^2)/(4π^2L), we keep M, b and L constant, and since g is constant, does that mean varying the T (Time Period) by increasing the angle will directly affect the I (Moment of Inertia)? Can I do an IA(Internal Assessment, basically an experimental investigation) on that?

@waelalghanami9093 4 жыл бұрын

Ah, a fellow IB student

@koolkataustin2961 4 жыл бұрын

@@waelalghanami9093 lol how's it going

@waelalghanami9093 4 жыл бұрын

@@koolkataustin2961 EE due in a week and I'm at 200 words. I'd say it's going pretty well.

@koolkataustin2961 4 жыл бұрын

@@waelalghanami9093 I have the exams that decide my predicted grade(which is what decides my uni) in 4 days, and I haven't started studying yet. Pretty good for me too.

@waelalghanami9093 4 жыл бұрын

@@koolkataustin2961 Good luck brother. What subjects are you taking?

@waqasmuneer7951 2 жыл бұрын

Sir please make a video of big idea of FEM if possible

@mohamedezeldin 7 жыл бұрын

Hallo Purdue, I would thank you for your good explaination but I have some notes on your work: 1- the experimental twist angle is approx more than 15° but the relation will not equal sin(°)=|=(°), if you need to apply this relation the angle should be close to zero. 2- your derivation was M.g.b^2.theta/(2L) at time 5:28 sec but at time 12:21 was M.g.b^2.theta/(L) (2 times than before why??)

@lipe9567 7 жыл бұрын

I had the same doubt, but I figured out why here. It happened because in the first part he derived the momentum of only one cable, and in the second equation(with the thetas) we need to use the sum of momentuns. That's why it's 2 times than before.

@brandontoledo6915 6 жыл бұрын

What happened to the two in the denominator?

@Rezwan47 6 жыл бұрын

Repeat the video and consider on (11:50) to (12:00)

@matiassantacruz5487 4 жыл бұрын

Damn....I was trying to find a way to derive an equation for a Bifilar Pendulum's time period based on the distance between files...

@MrLennon70 5 жыл бұрын

Can we get Period directly from g = 4(Pi^2)L/T^2 without measuring period manually using pendulum?

@koolkataustin2961 4 жыл бұрын

no, cause the 'g' may be inaccurate. you need to do the opposite, and confirm that g is acurate for your pendulum after measuring pendulum

@Joe0x7F 6 жыл бұрын

Great! Fantastic! Thank you!

@ovaisanwar8045 7 жыл бұрын

very helpful. Thank you

@SynytsiaAnton 7 жыл бұрын

Interesting!

@ajayjoseph4626 5 жыл бұрын

how do you theoretically calculate the moment of inertia of a funny shaped object? for example a quadcopter? it's not a solid piece of material. Do those suspended strings have to be parallel?

@chatchawanhannongbua494 6 жыл бұрын

Hello. How to measure moment of inertia of crankshaft?

@ahmedmasri7206 4 жыл бұрын

How did u find the uncertainty in the moment of inertia?

@magnussvommemann 6 жыл бұрын

Very good video and easily explained! Is there a reason you used so long strings?

@hassanmualla3693 6 жыл бұрын

With long strings, you can rotate the mass more while still getting low value for α. So assuming that sinα=α is possible.

@user-jv4nm4bt3d 4 жыл бұрын

if I want to measure the moment of inertia of a irregular shaped object , then how I can find the two points to connect the strings at the beginning? do I need to find the center of gravity first? if the center of gravity is not on the middle axis of the two strings, can we still use this math model?

@koolkataustin2961 4 жыл бұрын

You need to find the center of mass. You can use this math model, but the distance b must be measured from the center of mass. Refer to this image: www.google.com/url?sa=i&source=images&cd=&ved=2ahUKEwim7baK1oflAhUIi3AKHS21DHMQjRx6BAgBEAQ&url=https%3A%2F%2Fwww.researchgate.net%2Ffigure%2FUsing-the-bifilar-pendulum-method-to-measure-the-moment-of-inertia_fig2_2358471&psig=AOvVaw0tiWS_FGzyE_NVK1unHbUd&ust=1570452627778261

@davidwhitford4286 6 жыл бұрын

can I ask during the start of the proof when he uses the triangle why does b(\)/L=tan(a). Where does b(\) come from?

@rohitraj-ie2tk 4 жыл бұрын

b(/) is the arc length which by L is approximately sin (/)

@ctnry5190 5 жыл бұрын

Where did the theta=Ae^iwt come from?

@CompassionOverFear94 5 жыл бұрын

He assumed sinusoidal motion, of which can be described as theta=Ae^iwt. You don't have to know A or theta; it's just helpful for deriving the expression (A cancels out when these terms are inserted into the M=I(alpha) expression.