1. The Nature of Waves

2. Wave: Any disturbance that transmits energy through matter or empty space.

3. Question: Imagine your family has just returned home from a day at the beach. You had fun playing in the ocean under a hot sun. You put some pizza in the microwave for dinner, and you turn on the radio. Just then, the phone rings. It’s your friend calling to ask about homework. In the above scenario, how many different waves were present?

4. Answer: Believe it or not, there were at least five!!! –Water waves in the ocean –Light waves from the sun –Microwaves inside in the microwave oven –Radio waves transmitted to the radio –Sound waves from the radio, telephone, and voices

5. Medium: A substance through which a wave can travel (can be a solid, liquid, or gas)

6. Types of Waves The two main types of waves are: TransverseLongitudinal

7. Transverse Waves Particles in this kind of wave move across, or perpendicular to, the direction the wave is going. “moving across” and at “right angles”

8. Example: Shaking a rope “up and down” creates a transverse wave

9. The highest point of a transverse wave is called the “crest.”

10. The lowest point between each crest is called a “trough.”

11. Transverse Waves Trough Crest

12. Longitudinal Waves The particles of the medium vibrate back and forth along the path that the wave moves

13. Examples: Pushing a spring “back and forth” creates a longitudinal wave Sound waves

14. The parts of a longitudinal wave where the particles are crowded is called a “compression.”

15. A part where the particles are spread apart is called a “rarefaction.”

16. Longitudinal Wave compression rarefaction

17. Combinations of Waves A combination of transverse and longitudinal waves is called a “surface wave”

18. Properties of Waves

19. Properties of waves, such as the height of waves and the distance between crests, are useful for comparing and describing waves

20. Amplitude The maximum distance that the particles of a wave’s medium vibrate from their rest position

21. Question: What wave carries more energy – a wave with a large amplitude or a wave with a small amplitude?

22. Answer: A wave with a large amplitude carries more energy because it takes more energy to move the rope farther from its resting point.

23. Wavelength Distance between any two crests next to each other in a wave (usually measured in nanometers) 1,000,000,000 nm = 1 m

24. Wavelength: ---------------------------------------------------------------------------------------------------- Amplitude Rest Position Amplitude Wavelength

25. Frequency: Number of waves produced in a given amount of time Frequency is expressed in Hertz (Hz) Example: how many times a bobber in a lake bobs up and down

26. F. Y. I. Hertz is the Metric System derived unit of frequency and is equal to one wave per second.

27. (1Hz = 1/s) If two waves go by in 10 seconds, then the frequency is 2/10 s which =.2 Hz.

28. Wave speed: The speed at which a wave travels through a medium

29. Wave Equation: Wavelength (λ) Greek letter lambda Frequency (f) Wave speed (v) Wavelength X frequency = wave speed λ X f = v

30. F. Y. I. When a wavelength decreases (crests get closer together), the frequency (the number of waves produced in a given amount of time) increases. The opposite is true as well!!

31. Wave Interactions

32. Question: Why do planets shine so brightly?

33. Answer: The planets and the moon shine because light from the sun reflects off them.

34. Reflection Reflection happens when a wave bounces back after hitting a barrier.

35. All waves can be reflected. Water – You’ve seen it! Sound – echo Light – light waves from the sun are reflected when they strike the moon’s surface

36. Refraction The bending of a wave as the wave passes from one medium to another at an angle because the wave speed changes Example: Look at a pencil in a half-filled glass of water.

37. Diffraction A change in the direction of a wave when the wave finds an obstacle or an edge such as an opening Example: hearing music (sound waves) around a corner

38. Interference The combination of two or more waves that result in a single wave Constructive Interference – when the crests of one wave overlap the crests of another wave Destructive Interference – when the crests of one wave and troughs of another wave overlap

39. Standing Wave Certain parts of the wave are always at the rest position because of total destructive interference. The frequencies at which standing waves are made are called resonant frequencies.

40. Resonance Two objects naturally vibrate at the same frequency. Sound produced by one object causes the other object to vibrate.