00:03
All right, so i've loaded up the fet simulator like your instruction said to.
00:10
And if we go over to this moment of inertia tab, that's where we need to be.
00:15
And i tinkered a little bit before i started recording just to make sure i was doing it correctly.
00:20
So in instructions, if you look over here, we've got to change the y -axis.
00:27
And your instructor is asking you to change the y axis on the torque to a range of negative 20 to 20.
00:35
To change the range, you just use these buttons here.
00:38
So i'm going to keep it at that right there.
00:42
And then same with this.
00:43
You need to have it at negative 2 to 2 is what they're asking.
00:47
So i'll do that.
00:48
And then this one uses a b negative 1 ,000 to 1 ,000.
00:52
You'll have to push that button for quite a while to get it out to that range.
00:57
I wonder if it was, i'm thinking, i'm going to go, yeah, i guess we'll leave it at negative 1 ,000 to 1 ,000.
01:09
So i've set all those.
01:11
And we have these as our starting units.
01:15
And so the moment of inertia of a disk is one half mass times radius squared.
01:23
So the moment of inertia of this particular disc is going to be one half of this value, which is 0 .06 kilograms times radius square, which is 16.
01:34
So 0 .06 times 16 comes out to right under 1.
01:39
So it's like 0 .96.
01:42
Well, that's our moment of inertia right now is being rounded to the nearest 10th.
01:47
So it's one kilogram times meters squared.
01:50
So that's our moment of inertia.
01:52
We've got that setup.
01:53
It's right here.
01:55
I've also have the ability to take off some of these vectors.
01:59
But i'm going to leave them on there.
02:00
Notice, i assume that you've learned about centripetal force already.
02:05
Always the acceleration of an object that's playing around in a circle is pointed towards the center, and the velocity is tangent to that.
02:14
So that's centripetal force happening there.
02:17
Keep that bug on there.
02:18
Now what's the cause of it? it's the friction of the bug with the disk.
02:24
We want to know what's the torque going on on this disc when we push on it.
02:29
So if you come over here, like it says in instructions, you have to push on it.
02:34
Now i'm going to push on it slightly like that.
02:37
And notice that when i do that, i'm dragging my mouse.
02:40
So i'm pushing the left button on my mouse.
02:45
If you're using a pc, i don't know what it's like if i'm using a laptop or mac, but it's on a pc, the mouse left mouse button will get this going.
02:56
So if i want to slow this down, i can do this.
02:59
And notice how that's changing the graph.
03:02
Notice how it changes this graph, the blue line, and then this pink line down here.
03:07
Notice this does not change it up because we haven't done anything to the disk while we're doing on this.
03:14
It's an interesting fact that these two graphs are identical to each other, even though they're measuring different things.
03:22
That's telling us there's a direct relationship between these, which proves the second law motion, that the torque is equal to the moment of inertia times the angular.
03:33
Acceleration.
03:34
We learned in a linear, the linear world, it's f equals m .a.
03:39
Well, in the rotational world, it's torque equals moment of inertia times angular acceleration.
03:45
So that's the point of this lab.
03:48
To answer the questions, you need to come and try this out...