Define the radian
One radian is the angle subtended at the centre of a circle by an arc of length equal to the circle’s radius.
Define Displacement
Distance from equilibrium
Define Amplitude
Maximum displacement from equilibrium
Define period
The time for one complete oscillation
Define frequency
The number of oscillations per unit time
Define Angular Frequency
2pifrequency
Define Phase Difference
The fraction of an oscillation one wave leads or lags behind another wave
Define Simple Harmonic Motion
Acceleration is directly proportional to its displacement from its equilibrium position and acts towards the equilibrium position
What is the difference between a free oscillation and a forced oscillation?
Free has no external forces; forced has continual or repeated force applied.
Describe examples where resonance is useful
- Tuning radio: electrical signal in circuit forced by incoming radio waves
- Microwave cooker: water molecules forced to vibrate by microwaves (whose f matches nat. f of vibration of water)
- MRI: The atomic nuclei are made to resonate by radio waves & the rate of relaxation shows the type of molecule.
Describe examples where resonance is annoying
- Buildings in earthquakes: The building vibrates because of the energy from waves of earthquake.
- Positive feedback in amplification systems: If microphone held too close to speaker emitting waves of same f as m-phone so waves from speaker force amplifier to resonate.
- Components in engines: Driven by engine, components can resonate which can cause damage or cracking.
- Bridges: Energy is transferred from wind to bridge causing bridge to resonate.
For a system in resonance (3):
Natural f = driver f
Max amplitude
Absorbs greatest energy from driver
Examples of free oscillations:
Guitar string
Pendulum/Swing
Banging a drum
Examples of forced oscillations:
Engine vibrations are felt on the seat by the passenger
Buildings in earthquakes
Bridges in wind
