Free oscillation
Oscillations - OCR A-Level Physics
Key Definition
Free oscillation
An oscillation where the system vibrates at its natural frequency with no external driving force and no energy input after the initial displacement.
An oscillation where the system vibrates at its natural frequency with no external driving force and no energy input after the initial displacement.
Key Definition
Forced oscillation
An oscillation where an external periodic force continuously drives the system. The system oscillates at the driving frequency, not necessarily its natural frequency.
An oscillation where an external periodic force continuously drives the system. The system oscillates at the driving frequency, not necessarily its natural frequency.
Key Definition
Damping
The reduction in amplitude of an oscillation over time due to energy being transferred to the surroundings (usually as thermal energy through friction or drag).
The reduction in amplitude of an oscillation over time due to energy being transferred to the surroundings (usually as thermal energy through friction or drag).
- Light dampingThe reduction in amplitude (and energyThe capacity to do work. Measured in joules (J).) of an oscillation over time due to resistive forces such as friction or air resistance.: amplitudeThe maximum displacement of a point on a wave from its equilibrium (rest) position. Measured in metres (m). decreases gradually over many oscillations. PeriodThe time taken for one complete oscillation or wave cycle. Measured in seconds (s). barely affected. The amplitudeThe maximum displacement of a point on a wave from its equilibrium (rest) position. Measured in metres (m). envelope is exponential.
- Heavy dampingThe reduction in amplitude (and energyThe capacity to do work. Measured in joules (J).) of an oscillation over time due to resistive forces such as friction or air resistance. (overdamping): system returns to equilibriumAn object is in equilibrium when the resultant force on it is zero. The object is either stationary or moving at constant velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹.. very slowly without oscillating. No oscillations occur.
- Critical dampingThe reduction in amplitude (and energyThe capacity to do work. Measured in joules (J).) of an oscillation over time due to resistive forces such as friction or air resistance.: system returns to equilibriumAn object is in equilibrium when the resultant force on it is zero. The object is either stationary or moving at constant velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹.. in the shortest possible time without oscillating. Used in car suspension and door closers.
- The natural frequencyThe number of complete oscillations passing a point per unit time. Measured in hertz (Hz).The frequencyThe number of complete oscillations passing a point per unit time. Measured in hertz (Hz). at which a system oscillates freely when displaced from equilibriumAn object is in equilibrium when the resultant force on it is zero. The object is either stationary or moving at constant velocityThe rate of change of displacement. A vector quantity. Measured in m s⁻¹.. and released, with no external driving force. f_0 is the frequencyThe number of complete oscillations passing a point per unit time. Measured in hertz (Hz). at which a system oscillates freely without damping.
Examiner Tips and Tricks
- When sketching damping graphs: light damping shows oscillations with exponentially decreasing amplitudeThe maximum displacement of a point on a wave from its equilibrium (rest) position. Measured in metres (m). (the envelope is a decaying exponential).
- Critical damping returns to zero quickly with no overshoot.
- Heavy damping returns to zero slowly with no overshoot.