Chapter 20 Sound

1. ORIGIN OF SOUND  The frequency of a sound wave is the same as the frequency of the source of the sound wave. Demo - Oscillator and speaker

Range of Human Hearing 20 Hz - 20,000 Hz. infrasonic. Frequencies below 20 Hz are Frequencies above 20,000 Hz areultrasonic.

2. NATURE OF SOUND IN AIR Tuning Fork Strobed Tuning Fork Sound in air is longitudinal with Compressions (Condensations) and Rarefactions

3.MEDIA THAT TRANSMIT SOUND  Air is most common but is a poor conductor.  Solids and liquids are good conductors.  A medium is required.  Video - Vacuum PumpVacuum Pump

4.SPEED OF SOUND  Much slower than light –Light speed is so fast that we consider it infinite  Thunder and Lightning –Five second delay per mile  Depends on wind, temperature, humidity  Does not depend on frequency –Orchestra thanks you!

At 0 o C (dry air) v = 1090 ft/s = 750 mi/hr = 330 m/s increases with humidity increases with temperature increases with density How v varies: SPEED OF SOUND Calculator

5.REFLECTION OF SOUND  Occurs anytime waves change media. Example:Echoes prolonging of sound by reflection Example: Rumble of distant thunder (several reflections from different distances) Reverberation -

 What is not reflected is transmitted and absorbed. The study of sound properties is acoustics.

Walt Disney Concert Hall

6.REFRACTION OF SOUND When different parts of a wave front move at different speeds, the wave front will bend. This bending is known as refraction. It occurs when different parts of a wave front are traveling in different media.

Warm Air (sound travels faster here) Cool Air (sound travels slower here)

Other Examples Thunder and lightning Sometimes distant lightning is not heard well. Other times it is. Submarines and sonar Refraction due to thermal gradients can “hide” submarines. Ultrasound in medicine Ultrasound echo and dolphins

7.ENERGY IN SOUND WAVES  Energy in sound is weak when compared to the energy in light.  The human ear is a remarkable detector. 10 million people speaking at the same time produce approximately enough energy to light one flashlight.

 High sound frequencies in air lose their energies (converted to thermal energy) more easily than do low frequencies. That is why low frequencies can be heard farther away. ENERGY and FREQUENCY

9.NATURAL FREQUENCY  Demo - Drop Different Sounding Objects  Objects have natural frequencies at which they vibrate.  The natural frequency depends on elasticity and shape.

8.FORCED VIBRATIONS  Demo - Tuning Fork Touching a Table  Sound is intensified because of the larger surface area that can vibrate the air.  The surface is forced to vibrate at the frequency of the tuning fork.  Examples: Musical sounding boards

10.RESONANCE  Resonance occurs when we force a vibration at the natural frequency of the object.  Result - increased amplitude Examples:Swinging Marching on a bridge

Demo - Matched Tuning Forks Demo - Singing Glass Video – Breaking Glass Demo - Gravity Chimes Demo – Boomwhackers

Yankee Doodle (arranged by Anthony T.) Can-can

Submultiples of the natural frequency also produces resonance. Demo and 512 Hz Tuning Forks Tacoma Narrows Bridge Demo - Vibrating Rod Demo - Vibrating Plate Note:

11.INTERFERENCE  Defined in Chapter 19 –Superposition of waves occupying the same place at the same time  Demo - Oscillator & Two Speakers  Examples: Dead spots in theaters and music halls Anti-noise technology

Beats  Fluctuating loudness due to two tones of slightly different frequencies that are sounded together (tremolo)  It is an interference effect.  Beats/s = difference in frequencies  Musical instruments are tuned using beats.  Dolphins use beats and Doppler effect.

Demo - Guitar

RADIO BROADCASTS AM kHz to 1605 kHz FM -88 MHz to 108 MHz

Chapter 20 Review Questions

Frequencies of sound that are too high for the human ear to hear are called... (a) faster than the speed of sound (b) supersonic (c) infrasonic (d) ultrasonic (e) subsonic (d) ultrasonic

For the same temperature for air, does sound travel faster in humid Galveston or in dry El Paso? (a) Galveston (b) El Paso (c) same speed in either city (a) Galveston

The bending of sound through air of uneven temperature is called (a) reflection (b) refraction (c) interference (d) reverberation (e) resonance (b) refraction

Lightning is seen, then ten seconds later thunder is heard. Approximately, how far away in feet is the thunder cloud? (a) 10,500 (b) 5280 (c) 1050 (d) 5250 (e) 105 (a) 10,500

A 250 Hz tuning fork and a 260 Hz tuning fork are vibrating near each other. How many beats per second are heard? (a) 255 (b) 510 (c) 10 (d) 250 (e) 260 (c) 10