1. Waves Chapter 10

2. The Nature of Waves wave: repeating disturbance or movement that transfers energy through matter or space -examples: light, ocean, sound, earthquake, etc. -energy is transferred from one molecule to a neighboring molecule -all carry energy without moving the matter itself (boat moves, but does not travel) -all are produced by vibrations medium: material through which a wave travels -may be a solid, liquid or gas -not all waves need matter to travel through

3. Mechanical Waves mechanical waves: waves that travel only through matter Types: 1. transverse: matter in the medium moves back and forth at right angles to the direction that the wave travels -water waves travel horizontally as the water moves vertically up and down.

4. Mechanical Waves 2. compressional wave: matter in the medium moves in the direction that the wave travels -sound waves: when a noise is made nearby air molecules are pushed together by vibrations. -slinky: the wave carries energy, but not matter, forward along the spring. -also called longitudinal waves

5. Mechanical Waves 3. combination waves: not purely transverse or compressional -water waves: water moves back and forth, as well as up and down, creating crests and troughs.

6. Mechanical Waves 3. combination waves: not purely transverse or compressional -seismic waves: breaking crust vibrates, creating waves that carry energy outward. *can travel through Earth and along its surface *the more the crust moves during an earthquake, the more energy is released.

7. Nature of Waves Review Write the Q & A 1.What is a wave? 2.What are the two types of waves? 3.What type of wave does not need a medium? 4.What does a mechanical wave always travel through? 5.What is different about light waves and mechanical waves? 6.What direction does matter move in a compressional wave? In a transverse wave? 7.What is another name for a compressional wave?

8. Wave Properties Waves differ in several ways: 1.how much energy they carry 2.how fast they travel 3.how they look -transverse waves have alternating high points, called crests, and low points, called troughs.

9. Wave Properties -compression waves have no crests and troughs ~do have a region where the coils are close together (compression) and a region where the coils are far apart (rarefraction)

10. Wave Properties However, waves do have similar characteristics: 1. wavelength: distance between one point in the wave and the nearest point just like it -in a compressional wave is the distance between two neighboring compressions or two neighboring rarefractions (start to start or end to end) -in a transverse wave the distance between two crests, two troughs or node to node

11. Wave Properties 2. frequency: how many wavelengths pass a fixed point each second -unit is the hertz (1/s, Hz) -the frequency of a wave equals the rate of vibration of the source that creates it -as frequency increases, wavelength decreases

12. Wave Properties 3. period: how long it takes one wavelength to pass a point -as the frequency increases, the period decreases 4. wave velocity ( )  describes how fast the wave moves forward -light waves travel faster than sound waves -light waves travel faster in gases and empty space than in liquids and solids -sound waves travel faster in liquids and solids than in a gas -velocity = wavelength x frequency = f

13. Wave Properties Wave speed example 1: What is the speed of sound wave that has a wavelength of 2.00m and a frequency of 170.5 Hz? Leave space for answer

14. Wave Properties Wave speed example 2: What is the wavelength of wave that has a speed of 225m/s and a frequency of 112.5 Hz? Leave space for answer

15. Wave Speed Practice Show all work & units!!! 1. A wave traveling in water has a frequency of 500.0 Hz and a wavelength of 3.0m. What is the speed of the wave? 2. The lowest-pitched sounds humans can hear have a frequency of 20.0Hz. What is the wavelength of these sound waves if their wave speed is 340.0m/s? 3. The highest pitched sound humans can hear has a wavelength of 0.017m in air. What is the frequency of these sound waves if their wave speed is 340.0m/s?

16. Wave Properties amplitude: measure of the energy a wave carries -the more energy, the higher the amplitude -measured differently for compressional and transverse waves. *in compressional waves, it is related to how tight the compressions are ~the denser the material, the higher the amplitude

17. Wave Properties amplitude: measure of the energy a wave carries *in transverse waves, it is related to the distance from the crest or trough of the wave to the rest position of the medium. ~the higher the amplitude,the more energy it carries

18. Wave Properties Review 1. If a wave has a high point and a low point, is it a compressional or transverse wave? 2. What refers to the number of wavelengths that passes a fixed point each second? 3. Describe the difference between a compressional wave with a large amplitude and one with a small amplitude. 4. Calculate the frequency of a water wave that has a wavelength of 0.5m and a speed of 4.0m/s?

19. Behavior of Waves reflection: when a wave strikes an object and bounces off of it -all types of waves (including sound, water, and light waves) can be reflected angle of incidence: angle formed by the incident beam and the normal angle of reflection: angle formed by the reflected beam and the normal

20. Behavior of Waves normal: imaginary line perpendicular to the reflective surface Law of reflection: the angle of incidence is equal to the angle of refection

21. Behavior of Waves refraction: bending of a wave caused by a change in speed as it moves from one medium to another -larger the change in speed, the more the wave bends -when a wave passes into a material that slows it down, the wave is bent toward the normal.

22. Behavior of Waves -when a wave passes into a material that speeds it up, the wave is bent away from the normal. You may have noticed objects underwater seem closer to the surface than they really are. - light waves reflected from the swimmer’s foot are refracted away from the normal and enter your eyes

23. Behavior of Waves diffraction: object causes a wave to change direction and bend around it -refraction occurs when waves pass through an object, while diffraction occurs when waves pass around an object

24. Behavior of Waves The amount of diffraction that occurs depends on how big the obstacle or opening is compared to the wavelength -when an obstacle is smaller than the wavelength, the waves bend around it. -if the obstacle is larger than the wavelength, the waves have less diffraction.

25. Behavior of Waves interference: ability of two or more waves to combine and form a new wave -constructive interference: the waves add together because two crests or two troughs arrive at the same place at the same time ~Notice the amplitude of the new wave is equal to the sum of the amplitudes of the original waves.

26. Behavior of Waves interference: ability of two or more waves to combine and form a new wave -destructive interference: the waves subtract from one another because a crest from one wave meets a trough from another wave ~Notice the amplitude of the new wave is the difference between the amplitudes of the waves that overlapped.

27. Behavior of Waves standing wave: special type of wave pattern that forms when waves equal in wavelength and amplitude, but traveling in opposite directions, continuously interfere with each other. -waves seem to ‘stand still’; constant -Some instruments, like flutes, create standing waves in a column of air. resonance: process by which an object is made to vibrate by absorbing energy at its natural frequencies -if enough energy is absorbed, the object can vibrate so strongly that it breaks apart.

28. Behavior of Waves Review 1. Which behavior of waves allows you to hear a sound around a corner? 2. How is the energy carried by each wave changed when interference occurs? 3. When is the effect of diffraction the greatest? 4. State the law of reflection. 5. ______ is the bending of a wave as it passes from one medium to another. 6. How are the angle of reflection and angle of incidence related? 7. Why can you not just reach for a coin that is underwater?