SOUNDSonic Spectrum

the frequency range over which longitudinal waves occur

•well defined upper limit of about 109 Hz

•undefined lower limit-lowest recorded frequencies belong to earthquakes

Sound refers to the audio spectrumthe range of frequencies that the human ear can distinguish:

20 Hz 20,000 Hzinfrasonic ultrasonic

Hearing Ranges for sample mammals:

Note: Frequency is independent of intensity (“loudness”)!

Production of Sound:•Sound is produced by vibrations produced in a medium capable of transmitting the energy•There needs to be a source of a disturbance and an medium that has particles that behave in an elastic manner when transmitting the energy.•The more “elastic” the medium is, the more efficiently (faster) it will transmit the sound!

At 40° C, the speed of sound is about:

air346 m/s

H2 1340 m/s

water 1500 m/s

steel 5200 m/s

The Speed of Sound•the speed of sound through a medium varies with the temperature of the medium•when the temperature is higher, the particles have a greater kinetic energy (they move faster) and so transmit the energy more efficiently (quicker)

The speed of sound in air at 0° C is 331.5 m/s.•the speed will increase/decrease at (.6 m/s)/°C

What is the speed of sound at 20.0°C?

331.5 m/s + .6(20.0) = 331.5 + 12.0 = 343.5 m/s

On a day when the air temperature is 22.0°C, a man fires a rifle and hears the echo of his shot 3.00 s later. How far away is the wall the sound echoed off of?

v= 331.5 m/s + .6(22.0) = 344.7 m/s

t= 3.00 s/2 = 1.50 s

d = ?

d = v t= (344.7 m/s)(1.50 s) =

517 m

A tuning fork with a frequency of 262 Hz is measured to have a wavelength of 1.32 m. What must the air temperature in the lab be?

f = 262 Hz = 1.32 m

T = ?

v = f = (262 Hz)(1.32 m)

346 m/s

346 m/s - 331.5 m/s = 14.5 m/s

14.5 m/s

.6 m/s/°C= 24.2°C

On a day when the air is 23.0˚C, a child drops a rock down a well that is 78.6 m deep. How much time will pass until he hears it hit the bottom?

v = 331.5 m/s + (.6)(23.0)= 345.3 m/s

∆d = 78.6 m

∆t = ?

vi = 0 a = g

Down:

∆tr = 2∆d

g

= 2(78.6 m)

9.80 m/s2

= 4.00 s∆ts = ∆d/v

= 78.6 m

345.3 m/s= .228 s

∆t = ∆tr + ∆ts

= 4.23 s

1) A man fires a rifle in a valley with parallel walls on day when the air temperature in the valley is -10.0˚ C. He hears an echo off of one wall 2.00 s later and 2.00 after that he hears the echo off of the second wall. How far apart are the valley walls?

2) A man at the bottom of a mine shaft strikes two pipes together and a man at the top of the shaft hears it 0.26 s later. If the air temperature of the shaft is 18.0˚ C, how long will it take for the man at the top of the shaft to hear a dropped hammer hit the bottom of the shaft?

977 m

4.52 s

3) A sailor strikes the side of his ship just below the water line and he hears the echo off of the bottom of the sea in 1.84 s. What is the speed of sound in water if the sea floor is 1360 m below?

4) A buoy anchored in a bay has a bell on it. As the bell rings, the anchor chain simultaneously bangs on the buoy. A boat with recreational divers is anchored 895 m from the buoy. How much time elapses between when the observers on the boat hear the bell versus when the divers in the water hear the chain? The air temp. is 30˚ C and sound travels 1480 m/s in the water.