The Nature and Behavior of Waves

1. The Nature and Behavior of Waves Chapter 10: Waves

2. Learning Goals • Compare and contrast transverse and compressional waves. • Identify the parts of a wave.

3. What is a Wave? • Wave:a repeating disturbance or movement that transfers energy through matter or space • Molecules pass their energy on to neighboring molecules

5. What is a Wave? • Waves carry energy WITHOUT transporting matter • All waves are produced by something that vibrates • Examples: sound, light

6. Waves and Energy • Think of a pebble falling into a pool of water and ripples forming. • The pebble has energy because it is falling.

7. Waves and Energy • When the pebble splashes into the pool it transfers its energy to the nearby water. • The energy is then transferred from water molecule to water molecule.

8. Waves and Matter • Think about a boat on a lake. • The waves bump the boat but they don’t carry the boat along with it as they pass. • The waves don’t even carry the water – they just carry the energy forward.

9. Mediums • Medium: a material through which a wave travels • Can be solids, liquids, or gases • Waves that can only travel through mediums are called mechanical waves

10. Mediums • Not all waves need a medium • Example: light and radio waves can travel through space

11. Mechanical Waves • Mechanical waves: waves that can travel only through matter • There are two main types of mechanical waves: • Transverse • Compressional

12. Transverse Waves • Transverse waves: matter in the medium moves back and forth at right angles to the directions that the wave travels • Example: water waves

14. Compressional Waves • Compressional waves: matter in the medium moves in the same direction that the wave travels • Example: sound waves

16. Combinations • Some waves are a mixture of transverse and compressional waves. • An example is seismic waves, which move the Earth up and down and side to side.

18. Properties of Waves Chapter 10: Waves

19. The Parts of a Wave • Waves can differ in how much energy they carry and in how fast they travel. • Waves also have other characteristics that make them different from each other.

20. The Parts of a Wave • A transverse wave has alternating high points called crests and low points called troughs.

21. The Parts of a Wave • When you make compressional waves in a coiled spring, a compression is a region where the coils are close together.

22. The Parts of a Wave • The coils in the region next to a compression are spread apart, or less dense. This less-dense region of a compressional wave is called a rarefaction.

24. Wavelength • A wavelength is the distance between one point on a wave and the nearest point just like it.

25. Wavelength • For transverse waves the wavelength is the distance from crest to crest or trough to trough.

26. Wavelength • A wavelength in a compressional wave is the distance between two neighboring compressions or two neighboring rarefactions.

27. Frequency • The frequency of a wave is the number of wavelengths that pass a fixed point each second. • Frequency is expressed in hertz (Hz).

28. Wavelength and Frequency • As frequency increases, wavelength decreases. • The frequency of a wave is always equal to the rate of vibration of the source that creates it.

29. Wavelength and Frequency • If you move the rope up, down, and back up in 1 s, the frequency of the wave you generate is 1 Hz.

30. Wavelength and Frequency • The speed of a wave depends on the medium it is traveling through. • Sound waves usually travel faster in liquids and solids than they do in gases. • However, light waves travel more slowly in liquid and solids than they do in gases or in empty space.

31. Wavelength and Frequency • Sound waves usually travel faster in a material if the temperature of the material is increased.

32. Calculating Wave Speed • You can calculate the speed of a wave represented by v by multiplying its frequency times its wavelength.

33. v= speed (m/s) f= frequency (Hz) λ= wave length (m)

34. Practice • What is the speed of a wave that has a frequency of 3 Hz and a wavelength of 2 meters?

36. Practice • What is the frequency of a wave that has a wavelength of 20 m and a speed of 5 m/s?

37. Practice • What is the wavelength of a wave that has a frequency of 200 Hz and a speed of 350 m/s?

38. Amplitude and Energy • Amplitude, or a waves height, is related to the energy carried by a wave. • The greater the wave’s amplitude is, the more energy the wave carries. • Amplitude is measured differently for compressional and transverse waves.

39. Amplitude and Energy • Compressional Waves: • The amplitude of a compressional wave is related to how tightly the medium is pushed together at the compressions.

40. Amplitude and Energy • The denser the medium is at the compressions, the larger its amplitude is and the more energy the wave carries. • The closer the coils are in a compression, the farther apart they are in a rarefaction.

41. Amplitude and Energy • So the less dense the medium is at the rarefactions, the more energy the wave carries.

42. More dense Less dense

43. Amplitude and Energy • Transverse Waves: • The amplitude of any transverse wave is the distance from the crest or trough of the wave to the rest position of the medium.