1. Waves

2. Objectives Recognize that waves carry energy but not matter
Define mechanical waves
Distinguish between transverse and compressional waves.
CLE Investigate the properties and behaviors of mechanical and electromagnetic waves.

3. The Nature of Waves
Wave – is a repeating disturbance or movement that transfers energy through matter or space
Molecules pass energy on to neighboring molecules.
Waves carry energy without transporting matter

4. The Nature of Waves All waves are produced by something that vibrates
Medium – a material through which a wave travels
May be solid, liquid, gas or combination
Sound waves – medium is air
Ocean waves – medium is water

5. The Nature of Waves Not all waves need a medium to travel through.
Example: Light & radio waves (space)
Electromagnetic waves don’t need a medium (e.g. visible light)

6. Mechanical Waves
Mechanical waves – waves that can travel only through matter
2 types: transverse and compressional

7. Transverse Waves
Transverse waves – matter in the medium moves at right angles to the direction that the wave travels
Example: water waves

8. B. Transverse Waves Transverse Waves
medium moves perpendicular to the direction of wave motion

9. Water Waves

10. corresponds to the amount of energy carried by the wave
B. Transverse Waves
Wave Anatomy
corresponds to the amount of energy carried by the wave
wavelength
crests
amplitude
nodes
troughs

11. 2. Mechanical waves need a matter medium to travel through.
(sound, water, seismic)
3. Two basic types of waves:
a. Transverse
b. Compressional
(longitudinal)

12. The Nature of Waves
Compressional waves – matter in the medium moves in the same direction that the wave travels.
Example: Sound waves
Nearby air molecules pushed together by vibrations
Travel through water and wood
Particles pushed together and move apart
Vibration of eardrum

13. Sound Waves

14. The Nature of Waves
Combinations – not purely transverse or compressional;
Example: water waves, seismic waves
See Fig. 5
See Fig. 6 pg 330

15. Seismic Wave

16. Question 1 What is a wave? Answer
Section Check 1
Question 1
What is a wave?
Answer
A wave is a repeating movement that transfers energy through matter or space.

17. Which is carried by a water wave?
Section Check 1
Question 2
Which is carried by a water wave?
A. a boat on the surface
B. boat anchor submerged 50 m
C. energy
D. water molecules

18. Section Check 1
Answer
The answer is C. Waves carry energy without transporting matter from place to place.
FL: SC.A.2.4.6

19. Which type of wave does not need a medium?
Section Check 1
Question 3
Which type of wave does not need a medium?
A. electromagnetic
B. mechanical
C. ocean
D. sound

20. Section Check 1
Answer
The answer is A. Electromagnetic waves are made by vibrating electric charges and can travel through space where matter is not present.

21. How are sounds made?
When somebody vibrates their vocal chords or slams a door, air particles are pushed together. This starts a sequence of compressions in the air that make a wave.

22. How are sounds made?
The air particles pass the energy on to neighboring air particles. When the wave reaches your ear, it causes your eardrum to vibrate. Your inner ear sends signals to your brain, which your brain interprets as sounds.

23. Objectives
Given a diagram, be able to identify the parts of a transverse and a compression wave
Given an illustration, be able to identify the amplitude, frequency, and wavelength
CLE Investigate the properties and behaviors of mechanical and electromagnetic waves.

24. Wave Properties Ways waves differ How much energy they carry
How fast they travel

25. Wave Properties How they look Transverse waves have
crests – the highest points, and troughs – the lowest points
Compressional waves have dense regions called compressions and less dense regions called rarefactions

26. Crest vs Trough

27. Wave Properties
Wavelength – the distance between one point in the wave and the nearest point just like it
Frequency – how many wavelengths pass a fixed point each second

28. Wave Properties Expressed in hertz (Hz)
As frequency increases, wavelength decreases
The frequency of a wave equals the rate of vibration of the source that creates it

29. Wave Properties
Speed of wave depends on properties of the medium it is traveling through
Wave velocity describes how fast the wave moves forward.
Velocity =
wavelength X frequency

30. Wave Properties Light waves travel faster than sound waves
Sound waves travel faster in liquids and solids than in gases
Light waves travel faster in gases and empty space than in liquids and solids

31. Wave Properties Amplitude – a measure of the energy in a wave
The more energy a wave carries, the greater its amplitude

32. Wave Properties
Amplitude of compressional waves is related to how tightly the medium is pushed together at the compression

33. Wave Properties
The denser the compressions, the larger the amplitude is and the more energy the wave carries
The less dense the rarefactions, the larger the amplitude and the more energy the wave carries

34. Wave Properties Amplitude of transverse waves
The distance from the crest or trough of a wave to the normal position of the medium
Example: how high an ocean wave appears above the water level

35. Amplitude

37. In a thunderstorm, why do you see lightning before you hear the thunder?
Light waves travel much faster than sound waves.

38. Thunder & Lightning

39. The Behavior of Waves
Reflection occurs when a wave strikes an object and bounces off of it

40. All types of waves can be reflected
The angle of incidence of a wave is always equal to the angle of reflection

41. The Behavior of Waves
Normal – an imaginary line perpendicular to a reflective surface
Angle of incidence – the angle formed by the wave striking the surface and the normal

42. Angle of reflection – the angle formed by the reflected wave and the normal

43. Incidence – Reflection w/Normal

44. The Behavior of Waves
Refraction – the bending of a wave caused by a change in its speed as it moves from one medium to another

46. The Behavior of Waves
The greater the change in speed is, the more the wave bends
When a wave passes into a material that slows it down, the wave is bent toward the normal
When a wave passes into a material that speeds it up, the wave is bent away from the normal

47. Refraction of Light in Water
Light waves travel slower in water than in air. This causes light waves to change direction when they move from water to air or air to water.
When light waves travel from air to water, they slow down and bend toward the normal.

49. Prism refracts the light twice -once when it enters the prism and
again when it leaves the prism.

50. The Behavior of Waves
Diffraction – an object caused a wave to change direction and bend around it
If the obstacle is smaller than the wavelength, the wave diffracts a lot
If the obstacle is larger than the wavelength, the wave does not diffract much

51. The Behavior of Waves The larger the obstacle is compared to
the wavelength, the less the waves will diffract

52. Interference – the ability of two or more waves to combine and form a new wave

53. The Behavior of Waves
Waves pass right through each other and continue in their original direction
New wave exists only while the two original waves continue to overlap

54. The Behavior of Waves Constructive interference – waves add together
Destructive interference – waves subtract from each other

55. The Behavior of Waves
Standing waves – a wave pattern that stays in one place
Form when waves of equal wavelength and amplitude that are traveling in opposite directions continuously interfere with each other

56. The Behavior of Waves
Nodes – the places where two waves always cancel each other
Resonance – the ability of an object to vibrate by absorbing energy at its natural frequency

57. Nodes

58. How do you think wave behaviors apply to music?
Constructive interference causes sound waves to become louder; destructive interference causes sound waves to become more quiet. Standing waves create rich, even, constant tones in music.

59. Sonic Boom vs Boom Cone