Module 5 §3: Oscillations · Year 2
Simple Harmonic Motion
Revision notes on Simple Harmonic Motion for the OCR A-level Physics specification (H556). Free to read, with 4 practice questions in the app.
Simple harmonic motion (SHM) — oscillation in which the acceleration is directly proportional to the displacement from equilibrium, and always directed towards equilibrium.
a = −ω² x
The minus sign is the physics — it says the acceleration always points back towards equilibrium, opposite to the displacement. Without it the equation would describe something accelerating away, which is not an oscillation at all.
The two conditions — both must hold for motion to count as simple harmonic:
acceleration proportional to displacement, and
acceleration directed towards the equilibrium position.
Restoring force — since F = ma, the condition is equivalent to F = −kx: a restoring force proportional to displacement. Hooke's law has exactly this form, which is why a mass on a spring oscillates with SHM.
Equilibrium position — where the resultant force is zero. The oscillator passes through it at maximum speed, not at rest: displacement is zero there, but velocity is greatest.
Amplitude (A) — the maximum displacement from equilibrium.
Angular frequency (ω) —
ω = 2π / T = 2πf
The same symbol and definition as in circular motion, and not a coincidence: SHM is the projection of uniform circular motion onto a diameter, which is where the equations come from.
Isochronous oscillations — the period of SHM does not depend on the amplitude. A pendulum swinging through a small arc and one swinging through a larger arc take the same time per swing.
Example: this is what made pendulum clocks possible. As the swing gradually dies away, the period stays the same, so the clock keeps time even as the amplitude falls — a result that would be useless if the period depended on how far it swung.
4 questions on Simple Harmonic Motion
Reading is not revising. This topic has 4 questions in the app — multiple choice, calculations, and written answers marked against the mark scheme, point by point. Miss one and it comes back later with its options reshuffled, so you have to know it rather than remember where the answer sat.
- Every topic of OCR A-level Physics (H556)
- Flashcards and every equation, linked to the topic it comes from
- Full mock papers in the real paper structure
20 minutes a day is free. No card, nothing to cancel — and the paid version never renews itself either.
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