WavesWaves

• A wave is a rhythmic disturbance that carries energy through matter or space.

Two Categories of Waves

Mechanical Waves– A wave that requires a

medium (matter).

Electromagnetic Waves– (Coming Soon,

Chapters 16 – 19)

Types of Mechanical WavesTypes of Mechanical Waves

• Transverse–A wave that vibrates perpendicular

to the motion of the waves.

• Longitudinal–A wave that vibrates parallel to the

motion of the wave.

Types of Mechanical WavesTypes of Mechanical Waves

• Surface–A wave that is a combination of

both transverse and longitudinal waves (overall motion is circular).

Types of Mechanical WavesTypes of Mechanical Waves

• Amplitude – maximum displacement from equilibrium.– The crest (compression) is highest point of

the wave and the trough (rarefaction) is the lowest point of the wave.

• Wavelength – The distance of one complete wave cycle (oscillation).

Wave PropertiesWave Properties

• Frequency (f) – Number of complete oscillations in one second; measured in Hertz.

• Period (T) – The time elapsed in one complete wave cycle (oscillation).

• Wave speed (v) – The product of the wavelength and frequency or, the wavelength divided by the period.

Wave MeasurementsWave Measurements

• Reflection – the bouncing back of a wave as it encounters a boundary.

– Fixed point reflection– Free boundary reflection

Wave BehaviorWave Behavior

• Diffraction – the spreading of waves around a barrier or object.

Wave BehaviorWave Behavior

• Refraction – the change in the direction of a wave as it enters a different medium.

Wave BehaviorWave Behavior

Interference• Principle of Superposition – the

combination of two or more waves into a single wave.

– Constructive interference– Destructive interference– Standing waves (nodes & antinodes)

Wave BehaviorWave Behavior

• Sound waves are longitudinal pressure variations that are transmitted through matter.

• Sound is produced by vibrating objects.

Sound WavesSound Waves

• Sound Level (loudness) – The amplitude of a sound wave.– Measured in decibels (dB). A 20 dB increase

equals a 10 time increase in pressure amplitude.

• Pitch– Describes the frequency of vibrations.– More vibrations = higher pitch; less vibrations

= lower pitch.

Properties of Sound WavesProperties of Sound Waves

• The apparent change in the pitch of a sound as it moves towards or away from an observer

– Pitch increases as a sound moves toward an observer.

– Pitch decreases as a sound moves away from an observer.

The Doppler ShiftThe Doppler Shift

• Closed-pipe resonators– A resonating tube (column) with one closed

end and one open end.– Minimum resonance frequencies occur at

one-fourth of the wavelength, then at half-wavelength intervals.

– Column lengths of (1/4)λ, (3/4)λ, (5/4)λ, etc., will result in resonance.

Sound & MusicSound & Music

• Open-pipe resonators– A resonating tube (column) with both ends

open.– Minimum resonance frequencies occur at

one-half of the wavelength, then at half-wavelength intervals.

– Column lengths of (1/2)λ, λ, (3/2)λ, 2λ, etc., will result in resonance.

Sound & MusicSound & Music

• Fundamental (f1)

– The lowest frequency of resonance.

• Harmonics– Higher frequencies that are multiples of the

fundamental frequency.

• Octave– The difference in frequency of two musical

notes with ratio of 1:2.

Sound & MusicSound & Music

• Beats– Oscillations in wave amplitude.– The frequency of the beat is the magnitude of

the difference between the two frequencies.

Sound & MusicSound & Music