Waves and Sound Chapter 14 Characteristics of Waves

Waves and Sound Chapter 14

Characteristics of Waves: A rhythmic disturbance that carries energy. Medium: A material through which waves travel.

Transverse Wave A wave in which the medium moves at a right angle to the direction the wave is traveling.

Amplitude Crest Trough Wavelength

Crest Trough Crest: The top of the wave. Trough: The bottom or valley of the wave.

Amplitude: The greatest distance the particles in a wave rise or fall from their rest position. The energy by the wave depends on the amplitude.

Wavelength( - lambda, m): The distance between a point on one wave and the same identical point on the next wave.

v Wave Velocity(v, m/s): The distance traveled by any point on the wave in one second.

Frequency(f, Hz): The number of waves that pass a point in a second. Hertz(Hz): The unit used to measure frequency. One Hz is equal to one wave per second.

v velocity = wavelength X frequency v = x f

Example #1: A tuning fork has a frequency of 256 hertz. The wavelength of the sound produced by the fork is 1. 32 meters. Calculate the velocity of the wave. Given: = 1. 32 m Find: v f = 256 Hz Basic Equation: v = X f Solve: v = X f = (1. 32 m) X (256 Hz) v = 338 m/s

Example #2: A wave has a wavelength of 1. 20 meters. Its velocity is 0. 75 meters per second. What is the frequency of the wave. Given: = 1. 20 m v = 0. 75 m/s Find: f Basic Equation: v = X f Solve: f = v / = (0. 75 m/s) (1. 20 m) f = 0. 63 Hz

Homework #14 -1 Read & Take Notes Pages: 329 -333 Practice Problems: 1 -7 Page: 335 Due: 5/7/7

The Nature of Sound What is Sound? ? ? Sound is a Compression Wave traveling through matter.

Compressional Waves Compression Waves Matter vibrates in the same direction as the wave travels.

Compressional Waves Compression Rarefaction

Comparing Media

Speed of Sound is transmitted through matter. The Velocity of Sound depends on the

Sound travels at a velocity of 332 m/s in air at 0 C. • Sound travels faster through warm air than through cold air. • The velocity of sound increases about 0. 6 m/s for each degree in temperature. • At 20 C sound travels at 344 m/s. • Sound travels much faster through liquids and solids than through gases.

Speed of Sound Velocity of Sound through Various Substances at 0 C air 332 m/s water 1454 m/s wood 3828 m/s iron 5103 m/s stone 5971 m/s

Human Hearing Frequency of Sound 20 Hz to 20, 000 Hz. Sound above 20, 000 Hz - Ultrasonic Sound less than 20 Hz – Subsonic (Infrasonic)

Intensity and Loudness Intensity of Sound Depends on the amplitude of the wave. Loudness Describes a person’s response to sound intensity.

Loudness is measured in Decibels(d. B) For every 10 d. B change the sound doubles!! 70 d. B is twice 60 d. B 80 d. B is four times 60 d. B

Faintest Sound Heard Whisper 15 d. B Rustling Leaves 20 d. B Purring Cat 25 d. B Average Home 50 d. B Vacuum Cleaner 75 d. B Noisy Restaurant 80 d. B Power Mower 100 d. B Chain Saw 115 d. B ------Painful ------- Jet Plane Taking Off 0 d. B 120 d. B 150 d. B

The Doppler Effect The change in wave frequency caused by the motion of the sound source or the motion of the observer.

The Doppler Effect

The Doppler Effect

Homework #15 -1 PP: 1 -4 Page: 352 Section Review Page: 355 Due: 5/11/01

Music to Your Ears A back and forth motion is set up in a string, resulting in a regular vibration. The vibration is called a standing wave the location of the crests and troughs are always in the same place.

In a wind instrument, holes are opened and closed, changing the length of the vibrating column of air. This changes the size of the standing wave.

Noise Sound with no regular pattern or definite pitch.

Tone Quality The differences among sounds of the same pitch and loudness.

Musical Sounds Based on a series of notes called a musical scale.

Fundamental 262 Hz Frequency First 524 Hz Overtone Second 786 Hz Overtone Third Overtone 1048 Hz

Harmony Notes that sound pleasing together. The ratio of the frequencies of tones that are in harmony are small whole numbers. Notes that are one octave apart. Middle C and C 524/262 = 2/1 · Notes E and C 330/262 = 5/4 ·

Interference Constructive Interference Occurs when the compressions and rarefactions of two or more waves come together. Louder Sound

Interference Destructive Interference Occurs when a compression of one wave arrives at the same time as a rarefaction of another wave. Quieter Sound

Interference Beats The result of compressions and rarefactions of two slightly different frequencies reaching your ears together. Beats

Acoustics The study of the science of sound. Design auditoriums. Design communication systems. Study materials. Study hearing. . .

Reverberation The result of many different reflections of sound in a large room.

Homework #4 -20 SWUP 18 -4 Page: 521 Worksheet Due: 5/17/01