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

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Waves 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 Waves
Transverse A wave that vibrates perpendicular to the motion of the waves.

Types of Mechanical Waves
Longitudinal A wave that vibrates parallel to the motion of the wave.

Types of Mechanical Waves
Surface A wave that is a combination of both transverse and longitudinal waves (overall motion is circular).

Wave Properties 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 Measurements 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 Behavior Reflection – the bouncing back of a wave as it encounters a boundary. Fixed point reflection Free boundary reflection

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

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

Wave Behavior Interference
Principle of Superposition – the combination of two or more waves into a single wave. Constructive interference Destructive interference Standing waves (nodes & antinodes)

Sound Waves Sound waves are longitudinal pressure variations that are transmitted through matter. Sound is produced by vibrating objects.

Properties of Sound 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.

The Doppler Shift 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.

Sound & Music 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 & 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 & Music Fundamental (f1) Harmonics Octave
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 & Music Beats Oscillations in wave amplitude.
The frequency of the beat is the magnitude of the difference between the two frequencies.

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