1. 24.1 –Properties of Sound pp. 578 - 582
Chapter 24 –Sound
24.1 –Properties of Sound pp

2. SPEED OF SOUND Depends on the medium through which it is traveling.
Changes when the medium changes.
Sound travels faster in steel than in water.
Speed of sound depends on temperature. The cooler the temperature, the slower the speed of sound.

3. 24.1 The speed of sound
The speed of sound in normal air is 343 meters per second (660 miles per hour).
Sound travels through most liquids and solids faster than through air.
Sound travels about five times faster in water, and about 18 times faster in steel.

4. 24.1 The speed of sound
Objects that move faster than sound are called supersonic.
If you were on the ground watching a supersonic plane fly toward you, there would be silence.
The sound would be behind the plane, racing to catch up.

5. 24.1 The speed of sound
Passenger jets are subsonic because they travel at speeds from 400 to 500 mi/hr.

6. PITCH
The pitch of a sound is determined by the frequency of the sound wave.
High pitch = high frequency
Low pitch = low frequency

7. 24.1 The frequency of sound
Almost all the sounds you hear contain many frequencies at the same time.
Humans can generally hear frequencies between 20 Hz and 20,000 Hz.

8. FREQUENCIES YOU CANNOT HEAR
Sounds with frequencies lower than 20 Hz are called infrasonic.
“Infra” means “below”.
Sounds with frequencies higher than 20,000 Hz are called ultrasonic.
“Ultra” means “beyond”
Ultrasonic waves are used to clean jewelry and to remove ice from metal.

9. 24.1 The frequency of sound
Sounds near 2,000 Hz seem louder than sounds of other frequencies, even at the same decibel level.
According to this curve, a 25 dB sound at 1,000 Hz sounds just as loud as an 40 dB sound at 100 Hz.

10. THE DOPPLER EFFECT
For sound waves, the Doppler effect is the apparent change in frequency of a sound caused by the motion of either the listener or the source of the sound.

11. LOUDNESS Loudness is related to amplitude.
The higher the amplitude of the wave, the louder the sound is.
The lower the amplitude of the wave, the softer the sound is.
Loudness is measured in decibels (dB).

12. SEEING SOUNDS
An oscilloscope is used to graph representations of sound waves.

13. HOW IT WORKS
A microphone converts the sound waves into an electric current.
The oscilloscope converts the electric current into graphs. The highest point (crests) represent compressions of the sound wave; the lowest point (trough) represents rarefactions.