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Real Oscillators. … constant forces integrate EOM parabolic trajectories. … linear restoring force guess EOM solution SHM. … nonlinear restoring forces ?. nonlinear spring?. linear spring. F. F. x. x. 0. 0. The spring of air :. use Ideal Gas Law: PV=NRT.
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Real Oscillators … constant forces integrate EOM parabolic trajectories. … linear restoring force guess EOM solution SHM … nonlinear restoring forces ? nonlinear spring? linear spring F F x x
0 0 The spring of air : use Ideal Gas Law: PV=NRT Patm chamber volume: V=Ax WTF! (whoa there, fella) m EOM A +x Stable Equilibrium at xeq = NRT / (mg + APatm) P, V 0
Taylor Series Expansions: Turns a function into a polynomial near x = a Example:
Expand around x = -3: 2nd order 0th order 1st order
Expand around x = 2: 0th order 1st order 2nd order
Expand NRT/x around xeq: Is it safe to linearize it? Better check a unitless ratio. How about: (Yes, excellent choice Dr. Hafner!)
.. Displacement 5% of xeq: 0 .05 .0025 …. Perhaps you would prefer…. SHM with
-x Simple Pendulum: Stable Equilibrium: Length: L Mass: m Q Displace by Q: mg cosQ T mg cosQ sinQ mg cosQ EOM: mg Expand it! mg
Now express as a unitless ratio of the dependent variable and some parameter of the system: Displacement 5% of length: 0 .05 0 .0000625 … SHM with
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).