Sound

Production of Sound Waves

A. ParallelB. Perpendicular C. Circular

Sound waves are Longitudinal

Longitudinal means that the particles in the medium vibrate how compared to the wave motion?

Compression/Rarefaction

Characteristics of Sound Waves Audible Range: Range of sound the

average human can hear. Low Frequency: 20 Hz High Frequency: 20,000 Hz

What is the range of sound called that falls below the frequency of 20 Hz?

A. non-sonicB. infrasonicC. unsonicD. Antisonic

Infrasonic is the term used for a sound wave that falls below the 20Hz frequency.

Humpback whales communicate on infrasonic frequencies.

The term that describes sound waves above the 20,000 Hz frequency is called ultrasonic.

Dogs can hear ultrasonic frequencies. This is why a good dog whistle cannot be heard by humans.

If the speed of sound is 343 m/s, what is the wavelength of an ultrasonic wave with a frequency of 35,000 Hz?

.00980.01

Frequency determines the pitch of the sound. Whether the sound is a high or low pitch.

Ultrasonic waves produce ultrasonic images.

Speed of Sound Depends on Medium

Sound travels fastest through medium which are more dense. Why?

Sound is the vibration of particles in a substance. The closer the particles, the faster the transfer of energy.

Iron: 5130 m/s Water: 1490 m/s Air: 331 m/s @ 0° C

Why would the temperature of air effect the speed of sound in air?

A. because hot air rises.B. because the temperature adds

energy to the wave.C. because the particles in the air

move faster.

In Fact…..

The speed of sound in air increases by .6 m/s every °C the air temperature goes up.

So at room temperature, 20 °C, the speed of sound in that room is 343 m/s.

The temperature on a hot sunny day is around 30° C, what is the speed of sound in m/s?

349 0.1

Sound waves propagate in 3 dimensions.

Spherical wave fronts that are large distances away from the source appear to be plane waves.

The Doppler EffectRelative motion creates an Apparent change in frequency.

The Doppler Equation

sourcevvvv

ff

detector'

Vdetector: Positive if listener is moving toward sourceVdetector: Negative if listener is moving away from sourceVsource: Negative if source is moving toward listenerVsource: Positive if source is moving away from listener

A siren produces a frequency of 1500Hz. A runner who is passing the siren at 25 m/s hears the siren. What frequency is heard when the runner is going toward the siren? (Use 343 m/s for Vsound)

A. 1390 HzB. 1398 HzC. 1617 HzD. 1609 Hz

Loudness (Sound Intensity) The intensity or loudness of a sound

is perceived by a person’s sense of hearing.

Each person perceives sound differently.

The intensity scale numerically determines the “strength” of the sound.

Intensity Scale

Units: Watts/m2

2000 Watt speaker 1 meter away = 159.2 W/m2

24AreaPower intensity

rPower

A speaker has a intensity of .50 W/m2 at a distance of 6

meters away. What is the power output of the speaker?

226.20.5

Examples from the Intensity Scale

Decibel vs. Intensity Decibel scale is a Relative Loudness

scale. It is based off of

Created by A. G. Bell0

log10IIdB

Decibels For every power of 10 increase on

the sound intensity scale, the decibels increase by 10.

Scale starts at 0dB = 10-12 W/m2

Examples Decibel Scale

Decibels As stated earlier, decibels measure

the relative loudness of sound. For every 10 dB, the sound is 2 times

as loud. Therefore the difference between 0

dB and 120 dB is 4096 x louder.

Decibel If we have an object that is 20 dB

and want to make a 50 dB sound, how many more objects do we need?

– Rule: for every 10 dB added, we increase the # of objects by a power of 10.

Decibel So for our last example we went from

20 dB to 50 dB which is a difference of 30 dB.

30 dB is 3 sets of 10 Therefore for every set of 10 we

increase by a power of 10 1 = 20 dB, then 1000 = 50dB

Decibel What is we want to double the

number of objects?– Rule: if the number of objects are

doubled, then the dB increase by 3. Example: if there are 200 goats that

make 70 dB, then 400 goats make 73 dB.

IF one horn produces 50 dB how much louder is it if it

produces 80 dB?

A. 2B. 4C. 6D. 8

If there are 30 ants making a noise of 20 dB, how many ants

would make a 60dB noise?

A. 300000B. 30000C. 3000D. 300

40 bells make 70 dB. How many Bells are needed to make

96 dB?160000.0