00:02
Okay, so in this problem, they actually give you quite a bit to get started here, and they just want you to crunch the numbers, but let's explain what's happening anyways.
00:11
The net force is going to be equal to, well, what are the forces acting on in this situation? it looks like they don't show a picture here, but you've got the force of gravity acting down like this, and you've got a normal force acting up like this.
00:29
And so the net force is toward the center of the circle.
00:33
That's going to be your positive direction.
00:37
Away from the center is going to be your negative direction.
00:40
So let me write net force.
00:41
The net force is going to be the force of gravity minus force normal.
00:48
The way that they wrote it was mg minus normal at the top.
00:53
It's a different notation, but same exact thing.
00:57
In circular motion, we know that the net force is equal to mb squared over r.
01:04
Okay, so that's where this comes from.
01:07
They also, it looks like, added net top over, i'm sorry, not net top, normal at the top, over, and subtracted mv squared over r on both sides.
01:24
Okay, so we are going to be getting down to something like this, mg minus mv squared over r is equal to normal at the top.
01:35
I'm just solving for that unknown normal for.
01:39
And then lastly, factored out an m and a g.
01:48
So a little odd that they factored up the g too, but i guess that's not really a big deal.
01:54
So mg, you have a 1 from this term when you factor out mg, and then here you'd have a minus v squared over r.
02:05
But they also factored out a g that wasn't there, so that's going to go on the bottom like that...