Conservation of Angular Momentum

096 - Conservation of Angular Momentum

In this video Paul Andersen explains that the angular momentum of a system will be conserved as long as there is no net external torque. Both point objects and extended objects are covered along with several examples.

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Music Attribution
Title: String Theory
Artist: Herman Jolly

All of the images are licensed under creative commons and public domain licensing:

[kenz]

"The earth will gradually stop, but thats not something we have to worry about" OK LOL

[kabouch]

4:45 since the inertia of the system is doubled when there is no external torque is applied, angular velocity has to halve so that the total angular momentum of the system is conserved.

[rameenjamshed]

These videos are so helpful. Bozeman Science if my first priority when I am searching for physics, chemistry or other educational videos. All the lecture videos are well structured and perfectly explained.

[SkyWayMan]

Since you're doubling the disk mass, the speed "v" will half. Great video!

[throughmyeyes]

Here's the answer to his question because he doesn't seem to have posted it:


L = I * w_1
L = 2I * w_2 when you drop the second mass on, the moment of inertia doubles
I * w_1 = 2I * w_2 by conservation of angular momentum
w_1 = 2w_2
so
w_2 = (1/2) * w_1
that is, the angular momentum has halved

[kabouch]

0.57 since angular momentum is a vector product of the cross multiplication of two vectors(r and p), theta has to be included in the equation where theta is the counterclockwise angle from r to p

[alixhurtado]

OMG I LOVE You break it down so beautifully.

[vishantchauhan]

L=Iw=13X9.2=119.6
L=L'
119.6=Iw=26Xw
w=119.6/26=4.6 RAD/sec
so the w decreases to half

[vineethvenugopal]

I have been searching for such a wonderful explanation.❤❤
Thank you for clearing my doubt .

[justjames]

Really interesting video. Can you tell me how this would relate to creating speed in the golf swing because there is also centrifugal force acting on the clubhead and I'd like to understand how these two, c.o.a.m and centrifugal force work to create significant yet efficient clubhead speed.

[pharaoh]

So at 3:52 the 1.6Kg mass is moving at 3.0m/s. The string is pulled short so that at 4:37 the same 1.6Kg mass is moving at 6.0m/s. Got it. Now; assume that after 1 revolution in both of these cases the string is cut. Since Ke=1/2mv^2, I would expect the 1.6Kg mass from the short string to have 4 times the Kinetic Energy and travel 4 times as far as was the long string. That just does not seem right. Is it?

[nnat]

Hello Mr. Anderson, thank you for the great video. I don't seem to be finding the answer/how to work the final question. Would you be able to direct me, please?

[natsume]

I was so confused but i got it so listen for those who are confused lol: The answer is w=4.6 so its getting slower why? bc L= L' which cant be true when we have a bigger I yknow like when you spin and you spread your arms you kinda get slower so putting more mass in the center will make you faster. idk if you get it but i tried lol. Thank you for the video its so helpful

[SprintClub-xiyb]

How would you calculate something that is spiraling while spinning?

[parthpatel]

Disc will rotate with half of angular velocity!
True?

[sampathiraosimhachalam]

Angular velocity should be half of previous go get constant momentum

[SarveshKumar-mljd]

nice video ..
it was very helpful to me ...
can u leave revision notes after every video ... plz plz

[zhnsbh]

Since net torque is zero isnt it at rotational equilibrium and have constant angular speed??

[sharp]

I understood the narratives in the video (although English very bad) thank you very much

[wadeodonoghue]

In regards to conservation of angular momentum, using a rotational battery to store energy in contrast to chemical, heat etc, could be aided by expanding and contracting the rotating mass, as it directly effects torque, one can build a system where the spin meets the pull of the energy coming in, so as it absorbs energy it expands and slows down ready to absorb more energy speeding up, then at night when the energy is used it keeps contracting to keep it's speed constant as energy is reabsorbed into the house, the battery ready to absorb energy again the next day. This could help solve the solar energy storage problem. Your video made the Physics clear thank you. I just wonder if the math and materials would allow a viable battery, can it be made, would it work, it would be last very long by todays battery standards, possibly.