Light damping allows a system to oscillate with a gradually decreasing amplitude. Critical damping returns it to equilibrium in the shortest possible time without oscillation, while heavy damping also prevents oscillation but returns it more slowly.
This is part of IB Physics C.4 Standing waves and resonance and applies to both SL and HL.
How Damping Works
Damping removes mechanical energy from an oscillating system, usually through resistive forces such as friction or drag. Consequently, the amplitude decreases because energy is transferred to the surroundings, often as thermal energy.
The system's behaviour depends on the strength of the damping force:
| Type of damping | Motion after displacement | Typical example |
|---|---|---|
| Light damping | Oscillates about equilibrium with amplitude decreasing over time | A pendulum experiencing air resistance |
| Critical damping | Returns to equilibrium as quickly as possible without passing through it | A well-designed vehicle suspension or measuring instrument |
| Heavy damping | Returns to equilibrium without oscillating, but more slowly than with critical damping | A door closer moving through a very viscous fluid |
With light damping, energy is removed gradually, so the system crosses its equilibrium position repeatedly. With critical damping, the resistive effect is exactly sufficient to prevent overshooting while producing the fastest non-oscillatory return.
With heavy damping, the resistance is greater than the critical value. The strong resistance restricts the motion so much that the return to equilibrium takes longer.
A common misconception is that heavier damping always makes a system settle faster. This is incorrect: critical damping gives the fastest return without oscillation; excessive damping slows the system.
Exam Technique
For an IB describe question, state whether oscillations occur, how amplitude changes, and how quickly equilibrium is reached. When discussing resonance, explain that increased damping reduces the maximum amplitude and makes the resonance peak less pronounced.
