1. Ch. 20 Sec. 1 & 2 The Nature of Waves & Properties of Waves
Unit 4 Waves
Ch. 20 Sec. 1 & 2
The Nature of Waves & Properties of Waves

2. Waves
We often associate waves with bodies of water, but are there other situations where waves can exist?

3. Waves
wave - a rhythmic disturbance that carries energy without carrying matter
matter can move the energy (pass it along), but the matter does not move with the energy

4. Electromagnetic Waves
Types of Waves
Mechanical Waves
Electromagnetic Waves
mechanical waves - use matter to transfer energy
produced by the transfer of energy from molecule to molecule
the matter the waves travel through is called the medium
electromagnetic waves - do not use matter to transfer energy
produced by moving electrically charged particles
can travel in space/vacuum (no medium needed)

5. Electromagnetic Waves
Mechanical Waves
Electromagnetic Waves

6. Types of Mechanical Waves
Transverse Waves
Compressional Waves
compressional waves - matter in the medium moves in the same direction as the wave travels
no crests or troughs
ex. sound waves
transverse waves - matter in the medium moves at right angles to the direction the wave travels
high points are crests & low points are troughs
ex. water waves

7. Compressional MW vs. Transverse MW
COMPRESSIONAL MECHANICAL WAVE
TRANSVERSE MECHANICAL WAVE

8. IN SUMMARY…

9. Electromagnetic Waves
Mechanical Waves
(medium needed)
Transverse
(right angle)
Compressional
(same direction)
Electromagnetic Waves
(no medium needed)

10. Amplitude in transverse waves… in compressional waves…
amplitude - ½ the distance b/w a crest & a trough
in compressional waves…
amplitude - varies within a wave
amplitude is related to the energy of a wave (higher amplitude = more energy)
bright light & loud sounds have higher amplitudes

11. Wavelength in transverse waves…
wavelength - the distance from one crest to the next (or one trough to the next)
in compressional waves…
wavelength - the distance from one compression to the next (or one rarefaction to the next)

12. Frequency
frequency - # of wavelengths that pass a certain point in 1 sec.
unit = hertz (Hz) [wavelengths per second]
as wavelength ↑, frequency ↓ (assuming speed is equal)
inverse relationship
wavelength/frequency determines the color of light & the pitch of sound
low frequency = low pitch

13. Wave Speed
mechanical waves, such as sound, travel faster in mediums where atoms are closer together
travel faster in solids, slower in liquids, & slowest in gases  
electromagnetic waves, such as light, travel faster in mediums where atoms are farther apart
travel faster in gases, slower in liquids, & slowest in solids
light travels much faster through air than sound
light travels at 300 million m/s
sound travels at 340 m/s