Mechanical Waves

Mechanical wave

A disturbance that requires a material medium to propagate.

Transverse wave

A wave in which particles oscillate perpendicular to the direction of wave travel.

Longitudinal wave

A wave in which particles oscillate parallel to the direction of wave travel.

Wavelength

The distance between corresponding points on consecutive cycles.

Frequency

The number of complete wave cycles per second measured in hertz.

Period

The time taken for one complete cycle: T = 1/f.

Wave speed

v = fλ.

Amplitude

The maximum displacement from equilibrium.

Phase

The position of a point in the cycle of oscillation.

Superposition principle

When waves overlap the resultant displacement equals the sum of their individual displacements.

Constructive interference

Overlapping waves reinforce each other producing a larger resultant amplitude.

Destructive interference

Overlapping waves partially or completely cancel producing a smaller resultant amplitude.

Path difference

The difference between the distances travelled by two waves to reach the same point.

Constructive path difference

For coherent waves constructive interference occurs when path difference = nλ.

Destructive path difference

For coherent waves destructive interference occurs when path difference = (n + ½)λ.

Coherent sources

Sources that have the same frequency and a constant phase difference.

Doppler effect

The apparent frequency of a wave changes because of relative motion between source and observer.

Source approaching observer

An approaching source produces a higher observed frequency and shorter observed wavelength.

Source moving away

A source moving away produces a lower observed frequency and longer observed wavelength.

Resonance

Large-amplitude oscillations occur when a driving frequency is close to the natural frequency of a system.

Natural frequency

The frequency at which a system oscillates freely after being disturbed.

Standing wave

A pattern produced by interference between two waves of the same frequency travelling in opposite directions.

Node

A point on a standing wave that remains stationary.

Antinode

A point on a standing wave with maximum amplitude.

Diffraction

The spreading of waves as they pass through an opening or around an obstacle.

When diffraction is greatest

Diffraction is most significant when the opening or obstacle size is comparable to the wavelength.