1. Waves and Sounds Chapter 18

2. Waves and Sounds  Characteristics of Waves What are waves? What are waves? Rhythmic disturbances that carry energy through matter or space (a medium) Rhythmic disturbances that carry energy through matter or space (a medium) Medium – a material through which a wave transfers energy Medium – a material through which a wave transfers energy Examples: air, water, floor Examples: air, water, floor

3. Waves and Sounds  There are 2 types of waves: 1. Transverse wave: a. A transverse wave is a wave where the medium moves at right angles to the direction of travel

4. Waves and Sounds  Here is what a transverse wave might look like: Rest position Amplitude

5. Waves and Sounds  We can also label the different parts of this wave: b. a crest is the highest point of a wave c. a trough is the lowest point of a wave

6. Waves and Sounds d. Wavelength ( ) is the distance between the same point on 2 different waves. (crest to crest or trough to trough) e. Amplitude is the distance from crest (or trough) to rest position (how tall the wave is) Waves with more energy have large amplitudes Waves with more energy have large amplitudes Waves with less energy have small amplitudes Waves with less energy have small amplitudes

7. Waves and Sounds f. A pulse is a wave. g. The frequency (f) of a wave is the number of wave crests that pass a place each second. Frequency is measured in Hertz (Hz). Frequency is measured in Hertz (Hz). waves second

8. Waves and Sounds 2. Longitudinal Waves (Compression Waves) a. In a longitudinal wave the medium is displaced in the same direction as the motion

9. Waves and Sounds  We can also label the parts of this wave: b. A compression occurs when the spring is squeezed or crowded together (more dense) c. A rarefaction is the less dense part of the wave

10. Waves and Sounds d. A wavelength ( ) of a longitudinal wave consists of one compression and one rarefaction.

11. Waves and Sounds  We can also measure how fast waves travel. 3. The speed of sound waves depends on 2 things:

12. Waves and Sounds  The medium the wave is traveling through: Faster through solids and liquids Faster through solids and liquids Slower through air Slower through air  Temperature of the medium: Higher T’s = molecules move faster = collide more  faster sound waves Higher T’s = molecules move faster = collide more  faster sound waves

13. Waves and Sounds  We call this speed wave velocity (v).  Wave velocity describes how fast the wave moves forward. v = * f

14. Waves and Sounds  Helpful Hints: v f msms m Hz

15. Waves and Sounds  Example Calculations - Calculate the velocity of the wave: = 2 m = 2 m f = 4 Hz v = * f v = (2 m)(4 Hz) v = 8 m/s

16. Waves and Sounds  Calculate the frequency of the wave: v = 10 m/s = 5 m = 5 m f = v f = 10 m/s  5 m f = 2 Hz