… constant forces integrate EOM parabolic trajectories. … linear restoring force guess EOM solution SHM … nonlinear restoring forces ? linear spring x F nonlinear spring? x F Real Oscillators
The spring of air : P, V m A P atm +x 0 use Ideal Gas Law: P V=NRT chamber volume: V =Ax Stable Equilibrium at x eq = NRT / (mg + AP atm ) 0 0 EOM WTF! (whoa there, fella)
Taylor Series Expansions: Turns a function into a polynomial near x = a Example:
Expand around x = -3: 0 th order1 st order2 nd order
Expand around x = 2: 0 th order 1 st order 2 nd order
Expand N RT/x around x eq : Is it safe to linearize it? Better check a unitless ratio. How about: (Yes, excellent choice Dr. Hafner!)
Displacement 5% of x eq : …. SHM with Perhaps you would prefer…...
Simple Pendulum: Length: L Mass: m m g c o s T mg cos sin mg mg Stable Equilibrium: Displace by mg cos -x EOM: Expand it!
Derivatives:
Now express as a unitless ratio of the dependent variable and some parameter of the system: SHM with Displacement 5% of length: …
The world is not linear. However, one can use a Taylor expansion to linearize an EOM by assuming only small perturbations around a point of stable equilibrium (which may not be the origin).