5.3.3 Damping

• Damping: an oscillation is damped when an external force that acts on the oscillator has the effect of reducing the amplitude of its oscillations. (extra info: this is due to the energy loss to resistive forces such as drag or friction).
• Light damping: When damping forces are small and the period of the oscillations is almost unchanged.
• Heavy damping: when damping forces are large and the period of the oscillations increases slightly with the rapid decrease in amplitude.
• Very heavy damping: no oscillatory motion. Moves towards equilibrium position slowly.
• Critical damping: oscillator returns to equilibrium in shortest possible time.
• Free oscillation: the motion of a mechanical system displaced from its equilibrium position and then allowed to oscillate without any external forces.
• Forced oscillations: an oscillation in which a periodic driver force is applied to an oscillator.
• Resonance: the increase in amplitude of a forced oscillation when driving frequency matches the natural frequency of the oscillating system. (extra info: when the amplitude of oscillation rapidly increases, and if there is no damping, the amplitude will continue to increase until the system fails. As damping is increased, the amplitude will decrease at all frequencies, and the max amplitude occurs at a lower frequency).
• Natural frequency: the frequency of a free oscillation.
• The system can be filmed and the amplitude value recorded from video stills, as it can be difficult to determine this whilst the mass is oscillating.
• Suspend a mass between two springs attached to an oscillation generator and use a ruler parallel with the spring-mass system to record the amplitude.
• Since drag force due to the air damps the system, the amplitude should not continue to increase until the point of the system failure.
• Increase the frequency of the generator slowly so that the amplitude increases, reaching max amplitude when the driver frequency is the same as the natural frequency of the system (after which, increasing the frequency will decrease the amplitude).
• With a diagram to help, explain the difference between light damping, heavy damping and critical damping.

  Light damping occurs naturally (eg. pendulum oscillating in air), and the amplitude decreases exponentially (but time period remains constant as A and T are independent). When heavy damping occurs (eg. pendulum oscillating in water) the amplitude decreases dramatically. In critical damping (eg. pendulum oscillating in treacle) the object is stopped in as short a time as possible without overshooting equilibrium.