Waves: Transverse and Longitudinal, Measuring and Interactions

1. Ch. 14 - Waves • Waves • Transverse waves • Longitudinal waves • Measuring waves • Wave Interactions

2. A. Waves • Waves • rhythmic disturbances that carry energy through matter or space • Medium • material through which a wave transfers energy • solid, liquid, gas, or combination • electromagnetic waves don’t need a medium (e.g. visible light)

3. A. Waves • Waves that require a medium are called mechanical waves • Almost all waves are mechanical waves except light waves (we will learn about these next chapter)

4. A. Waves • Waves transfer energy • Energy= the ability to exert force over a distance • Also known as the ability to do work

5. A. Waves • Energy may spread out as a wave travels • Think of when you throw a stone in a pond • It makes circles called wave fronts • Each wave front has the same amount of energy, just over a larger distance • Sound waves travel in spheres

6. A. Waves • Waves are related to vibrations • Most waves are caused by vibrating objects • In mechanical waves, the particles in the medium also vibrate as the waves passes through the medium

7. A. Waves • Vibrations involve transfer of energy • Whenever a spring is expanded or compressed, it is exerting a force that pushes the mass back almost to the original position • As a result, the mass will continue to bounce up and down • This type of vibration is called: Simple Harmonic Motion

8. A. Waves • Sometimes, energy does not just bounce up and down • A vibration that fades out as energy is transferred from one object to another is called: • Damped Harmonic Motion

9. A. Waves • Two Types: Longitudinal & Transverse

10. B. Transverse Waves • Transverse Waves • medium moves perpendicular to the direction of wave motion • Like the wave in a stadium • Light waves are transverse

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

12. Crest= Highest point in a wave • Trough=lowest point in a wave • Amplitude=the maximum distance that the particles of a wave’s medium vibrate from their rest position • Wavelength=distance from any point on a wave to an identical point in the next wave • Period=time it takes to complete a cycle or wave oscillation to occur

13. C. Longitudinal Waves • Longitudinal Waves (a.k.a. compressional) • medium moves in the same direction as wave motion • Sound waves are longitudinal

14. compression wavelength rarefaction wavelength C. Longitudinal Waves • Wave Anatomy Amount of compressioncorresponds to amount of energy AMPLITUDE.

15. 1 second D. Measuring Waves • Frequency( f ) • # of waves passing a point in 1 second • Hertz (Hz) • shorter wavelength  higher frequency  higher energy

16. D. Measuring Waves • Velocity ( v ) • speed of a wave as it moves forward • depends on wave type and medium v = × f v: velocity (m/s) : wavelength (m) f: frequency (Hz)

17. D. Measuring Waves • Speed (velocity) of waves depends on medium • Why?Kinetic Theory • In gases, molecules are farther apart so has to go through lots of empty space. Waves do NOT travel as fast in gases • In liquids, molecules are closer together. Waves are faster in liquids than in gases • In solids, molecules are really close together, these are the fastest moving waves.

18. D. Measuring Waves v f λ

19. v f  D. Measuring Waves • EX: Find the velocity of a wave in a wave pool if its wavelength is 3.2 m and its frequency is 0.60 Hz. WORK: v =  × f v = (3.2 m)(0.60 Hz) v= 1.92 m/s GIVEN: v = ?  = 3.2 m f = 0.60 Hz

20. v f  D. Measuring Waves • EX: An earthquake produces a wave that has a wavelength of 417 m and travels at 5000 m/s. What is its frequency? WORK: f = v ÷  f = (5000 m/s) ÷ (417 m) f= 12 Hz GIVEN:  = 417 m v = 5000 m/s f = ?

21. E. Wave Interactions • Reflection: • The bouncing back of waves when they hit a surface that they do not go through • If waves reflect at a free boundary • The reflected wave is exactly like original wave except traveling in the opposite direction

22. E. Wave Interactions • Reflection: • If the wave is ATTACHED to something, then it is not a free boundary • The wave will reflect and turn upside down

23. E. Wave Interactions • Reflection, Diffraction, and Refraction • Diffraction: • A change in the direction of a wave when the wave finds an obstacle or an edge, such as an opening

24. E. Wave Interactions • Reflection, Diffraction, and Refraction • Refraction: • The bending of a wavefront as the wavefront passes between two substances (mediums) which the speed of the wave differs

25. E. Wave Interactions • Interference: • The combination of two or more waves of the same frequency that results in a single wave • Two types: Constructive & Destructive

26. E. Wave Interactions • Constructive interference: • Any interference in which waves combine so that the resulting wave is bigger • Constructive Interference increases amplitude

27. E. Wave Interactions • Destructive interference: • Any interference in which waves combine so that the resulting wave is smaller than the largest of the original waves (may cancel out completely) • Destructive Interference decreases amplitude

28. E. Wave Interactions • Waves can also interfere another way. • Suppose you send a wave down a rope tied to a wall at the other end. The wave is reflected from the wall and travels back along the rope • If you keep doing this, the waves traveling forward will interact with those traveling back

29. E. Wave Interactions • Standing waves can form when a wave is reflected at the boundary of a medium • Interference of the original wave with the reflected wave causes the medium to vibrate in a stationary pattern that resembles a loop or pattern of loops • They have antinodes and nodes

30. E. Wave Interactions • Node=point(s) with no vibration • This is the point of complete destructive interference • Antinode=point(s) of maximum vibration • This is the point of complete constructive interference