00:01
So i think even though it doesn't say it explicitly that we're supposed to take gravity into account.
00:06
We have a particle of mass m that is moving on the surface of a paraboloid that's defined like this.
00:20
We're going to treat that as a constraint.
00:24
So our lagrangian is t -mi -sv.
00:29
I'm going to use cylindrical coordinates.
00:40
Okay.
00:40
So our constraint then is that row squared is a times z and our potential energy function, our v actually, our gravitational potential is mgz.
01:01
So that it's z equals zero, the potential energy is zero.
01:08
So this is half m, row dot squared plus roe squared, phi dot squared minus, or plus z dot squared minus mgs.
01:24
That's our lagrangian.
01:28
All right.
01:44
So we go and find our lagrangian equations, partial l with respect to row dot.
02:12
So we get the lagrangian equations.
02:34
And then that has to equal the derivative of this with respect to row, it's called this f with our negrange multiplier.
02:54
Actually, i'm going to write an f not like that, like this.
03:11
And then the phi part, row squared phi dot, and there's no phi dependence.
03:28
So you've got d by dt or, there's our second equation, and our constraint doesn't depend on phi...