13Class 11 Physics

Oscillations formulas

Simple harmonic motion formulas for Oscillations. Everything follows from a = −ω²x, so identify ω first.

Motion

Displacement
x=Asin⁡(ωt+ϕ)\displaystyle x = A\sin(\omega t + \phi)
Velocity
v=ωA2−x2\displaystyle v = \omega\sqrt{A^2 - x^2}

Largest at the mean position, where v = Aω.

Acceleration
a=−ω2x\displaystyle a = -\omega^2 x

Largest at the extremes, where |a| = Aω².

Angular frequency
ω=2πν=2πT\displaystyle \omega = 2\pi\nu = \frac{2\pi}{T}

Energy

Kinetic energy
K=12mω2(A2−x2)\displaystyle K = \tfrac12 m\omega^2(A^2 - x^2)
Potential energy
U=12mω2x2\displaystyle U = \tfrac12 m\omega^2 x^2
Total energy
E=12mω2A2\displaystyle E = \tfrac12 m\omega^2 A^2

Stays constant.

Common systems

Spring and mass
T=2πmk\displaystyle T = 2\pi\sqrt{\frac{m}{k}}
Simple pendulum
T=2πLg\displaystyle T = 2\pi\sqrt{\frac{L}{g}}

For small angles.

Springs in series
1k=1k1+1k2\displaystyle \frac{1}{k} = \frac{1}{k_1} + \frac{1}{k_2}
Springs in parallel
k=k1+k2\displaystyle k = k_1 + k_2

Where students slip up

  • Thinking mass changes a pendulum's period. It doesn't, though it does change a spring's.
  • Confusing ν and ω. ω = 2πν, and it's a common factor-of-2π slip.
  • Assuming energy oscillates at the same frequency as displacement. KE and PE oscillate at twice that frequency.

Try it on your weakest chapter.

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