Class 14: Perturbations to a known solution

Before class, watch the lecture material linked below
Then post questions or comments (or respond to others) on Piazza (access via Canvas or from the direct link on the course page)
Check yourself via Check Yourself 14 (by 11:59pm on Mon Oct 19th)
In class, we'll work on examples of these ideas:
After class, complete the homework

Videos:
V01 (Sa)  |  Weakly nonlinear oscillator  (All)  |  8 min
V02 (St)  |  Finding the equations for radius and phase  (11:30 to 16:54) |  5 min
V03 (St)  |  Slow and fast timescales of the system  (17:27 to 22:30) |  5 min 
V04 (St)  |  Averaging out the fast timescale  (22:30 to 29:59)  |  7 min
V05 (St)  |  Time derivative of a running average  (30:41  to 34:01)  |  3 min
V06 (St)  |  Diff eqs for average values  (34:01 to 41:31)  |  7 min
V07 (St)  |  Applying average method to vdP for r eqtn  (41:42 to 57:10)  |  16 min
V08 (St)  |  IDing behavior in vdP eqtn  (57:02 to  1:09:40)  |  13 min
V09 (St)  |  (optional)  Applying method to Duffing  (1:09:45 to end)  |  7 min

Summary:
Intro by Sarah then almost all of Steve's lecture 11 (final example is optional)