3.6.1.4
Resonance has useful and destructive applications
Forced Vibrations & Resonance — AQA A-Level Physics
Useful applications
- Organ pipes: air resonates in the pipe, setting up a stationary waveA wave pattern formed by the superposition of two progressive waves of the same frequencyThe number of complete oscillations passing a point per unit time. Measured in hertz (Hz). and amplitudeThe maximum displacement of a point on a wave from its equilibrium (rest) position. Measured in metres (m). travelling in opposite directions. EnergyThe capacity to do work. Measured in joules (J). is not transferred along a stationary wave..
- Radio tuning: the electrical circuit resonates at the frequencyThe number of complete oscillations passing a point per unit time. Measured in hertz (Hz). of the chosen broadcast.
- Barton's pendulums: a driving pendulum of length L causes the pendulum of the same length to oscillate with maximum amplitudeThe maximum displacement of a point on a wave from its equilibrium (rest) position. Measured in metres (m)..
Destructive effects
- A wine glass shattering when exposed to a sound at its natural frequencyThe number of complete oscillations passing a point per unit time. Measured in hertz (Hz).The frequency 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..
- Bridges oscillating dangerously when the driving frequency (e.g. wind, marching soldiers) matches the natural frequencyThe frequency 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..
- Vibrations in car interiors at certain engine speeds.
Barton's pendulums
- Pendulums shorter than L oscillate in phase with the driver.
- The pendulum equal to L oscillates pi/2 (90 degrees) out of phase with the driver (resonanceThe condition where the driving frequency matches the natural frequency of a system, causing maximum amplitude of oscillation and maximum energyThe capacity to do work. Measured in joules (J). transfer.).
- Pendulums longer than L oscillate pi (180 degrees) out of phase with the driver.