00:01
All right, so we're giving a multiple choice question about a girl on a merry -go -round.
00:03
She goes toward the center of the merry -go -round.
00:06
So this merry -go -round is spinning with an angular velocity, and you got the girl on there, and we'll just call her m for a mass, and she's toward the edge, and then she moves in toward the center, like this.
00:24
And the concept that they're asking about here is angular momentum.
00:27
Angular momentum for a closed system is conserved, meaning the initial angular momentum is equal to the final.
00:35
An angular momentum consists of rotational inertia, which is i, times angular velocity, which is omega.
00:47
So what's going to happen in this situation is the rotational inertia of the system is going to go down.
00:53
When she moves toward the center, let me actually take one step back.
00:58
So i is going to be equal to some version.
01:02
Of m r squared.
01:04
So i'm going to call it n mr squared and then n m r squared.
01:15
And n can be any number.
01:16
Like it could be a fraction like one half or something or just one or whatever.
01:22
In this problem that what's going to happen effectively is the radius for her is going to go down because she's going to go toward the center of the circle.
01:33
So the rotational inertia is going to go down.
01:37
So when that happens, the angular velocity needs to go up in order to account for that change, because the total rotational inertia stays the same...