1. Sound
Sound Waves

2. The Production of Sound Waves
Sound waves are caused by vibrations
The vibrating object has regions of air with relatively high density and low density around it
High density areas – compressions
Low density areas – rarefactions
Sound waves are longitudinal waves
They have compacted areas (compressions) and expanded areas (rarefactions)

3. The Production of Sound Waves

4. The Production of Sound Waves

5. Characteristics of Sound Waves
Humans can hear in a limited frequency range – between 20 and 20,000Hz
Audible sound waves
Infrasound – any sound consisting of waves with frequencies lower than 20Hz
Ultrasound – any sound consisting of waves with frequencies higher than 20,000Hz

6. Characteristics of Sound Waves
Pitch – the perceived highness or lowness of a sound, depending on the frequency of sound waves
Faster vibrations lead to higher pitch
Higher frequency equals higher pitch

7. Characteristics of Sound Waves
Ultrasound is used in sonar systems for boats and bats
Can produce an image
Sonar – a system that uses reflected sound waves to determine the distance to and location of objects
Uses the formula distance = speed * time
d=vt
Ultrasound is also used in medicine
Sonograms to look inside a body to view internal organs
Don’t harm living cells like X-rays

8. Characteristics of Sound Waves
Speed of sound depends on the medium
Sound travels fastest through solids
Sound travels slowly through gases
Sound travels faster in hot temperatures than in cold temperatures
Difference is due to ease of particle collisions in solids at high temperatures
Certain solids slow down sound waves
Rubber

9. Characteristics of Sound Waves

10. Characteristics of Sound Waves
Sound waves propagate (spread) in all directions, three-dimensionally, from the source of the vibrations
Centers of compression surrounding the source are called wave fronts
Radial lines perpendicular to the wave fronts are called rays
Indicate direction of wave motion
At large distances, spherical wave fronts appear to be located on a single plane
Plane waves

11. Characteristics of Sound Waves

12. The Doppler Effect
Frequencies change when the source of the wave is moving
Doppler effect – a frequency shift that is the result of relative motion between the source of waves and an observer
Frequency and pitch increase when the source is closer
Blue shift
Frequency and pitch decrease when the source is further away
Red shift
Present in all waves

13. The Doppler Effect