A2 Level · Topic 17.3
A-Level 9702 / Topic 17 / A2

Damping, driving, and resonance.

Real oscillators lose energy and can be driven. Those two ideas, damping and forcing, meet in resonance, the dramatic amplitude growth that engineers must both exploit and avoid.

The key idea

Resistive forces damp an oscillation, removing energy and reducing amplitude. A driven oscillator shows resonance, a maximum amplitude, when the driving frequency equals the natural frequency; damping lowers and broadens the resonance peak.

amplitude decays (energy lost to damping) x t
Fig. 1 — Damping removes energy each cycle, so the amplitude decays within an envelope while the period stays nearly constant
Section 01

Free, damped, driven.

A real oscillator loses energy to resistive forces and its amplitude decays: it is damped. Drive it with a periodic force, though, and something striking happens near one special frequency. The simulation lets you sweep the driving frequency to find the resonance peak and then watch damping flatten it.

Section 02

Damping types and resonance.

Light damping lets the oscillations continue with a slowly decaying amplitude; critical damping returns the system to equilibrium in the shortest time without oscillating; heavy damping returns it slowly without oscillating. A driven system shows resonance, a maximum amplitude, when the driving frequency equals the natural frequency. Increasing the damping lowers and broadens the resonance peak and shifts it slightly lower in frequency.

Stage 1 · Learn

Check what the sim just showed you

Four quick checks on damping, its types, and resonance. Each correct answer earns XP and lights this skill on your star map.

Quick check+10 XP

Damping of an oscillation is caused by:

Quick check+10 XP

Critical damping is the case in which the system:

Quick check+10 XP

Resonance, the maximum amplitude of a driven oscillator, occurs when the driving frequency is:

Quick check+10 XP

Increasing the damping of a driven system makes the resonance peak:

Examiner trap

Critical damping returns the system to equilibrium fastest without oscillating, while heavy damping is slower, do not swap them. Resonance is sharply peaked at the natural frequency only when damping is light; more damping lowers and broadens the peak and shifts it slightly below the natural frequency. Resonance can be useful (tuning) or destructive (structures in wind or earthquakes).

Skill unlocked

Damping and resonance

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Stage 2 · Topic Paper 4 practice (all lessons)
All lessons in this topic
Original Paper 4 structured questions spanning every lesson in this topic, with full worked solutions.