Oscillations and Waves

Forced Oscillations and Resonance

Damping

- Caused by resistive forces that always oppose motion e.g. friction

-Energy is dissipated by these forces. E.g. friction or magnetic damping can result in kinetic energy being dissipated as heat energy flows from the system.

- Damped systems do not describe SHM.

Degrees of damping

- under damped: this means the body will oscillate before coming to rest at the equilibrium position.

-critically damped: the body will come to rest at the equilibrium position in the shortest possible time, without oscillating.

- over damped: this means the body will take longer to come to rest

undercriticalover

Resonance

• Natural frequency: the frequency at which a body will freely oscillate at if plucked or banged or otherwise set in motion.

• Forced oscillations: these occur when a ‘driver’ oscillating body causes another body (the ‘driven’ body) to oscillate at the same frequency (not necessarily its natural frequency).

• Resonance: This occurs when the forced vibration frequency of the driver is equal to a driven objects natural frequency.

Resonance of a text book

Ph

ysics

Resonance of a mass on a spring

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Frequency Adjust

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Frequency range

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Frequency

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E.g. The Tacoma narrows suspension bridge

- Video clip

E.g. Breaking a wine glass using resonance

-You tube clip

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