00:01
Okay, we have a pendulum with a spring, and i'm gonna call the length of the pendulum r, which is the length of the spring.
00:12
L is the unstretched length of the spring, plus some coordinate x, and our angle is theta.
00:24
So the kinetic energy would be this, but remember r is l plus x.
00:33
The potential energy has a spring term and a gravity term looks like that, where we're assuming the zero of gravitational potential is up here at the top, and r dot is just x dot, because r is l plus x and l is constant.
01:05
So i can write the kinetic energy like this, and then my lagrangian.
01:20
Don't confuse the l, which is the length of the spring, with the l, which is the lagrangian, okay? we'll take some derivatives and construct our equations...