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UNIT 5: VIBRATIONS, WAVES & SOUND. Waves and Oscillations Pendulum swinging back and forth shows how oscillations can create waves.

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Presentation on theme: "UNIT 5: VIBRATIONS, WAVES & SOUND. Waves and Oscillations Pendulum swinging back and forth shows how oscillations can create waves."— Presentation transcript:

1 UNIT 5: VIBRATIONS, WAVES & SOUND

2 Waves and Oscillations Pendulum swinging back and forth shows how oscillations can create waves.

3 WAVES Energy transfer: by doing work, by heat, or by waves! Wave: a disturbance (vibration) that travels mechanical waves require a material medium (solid, liquid, or gas) – particles vibrate in simple harmonic motion (water, sound, earthquake waves) 2 types – transverse and longitudinal electromagnetic waves travel through a material or a vacuum – vibrating electric and magnetic fields (radio, microwave, infrared, visible light, ultraviolet, x-ray, gamma rays)

4 WAVES Transverse waves: vibrations are perpendicular to wave direction

5 WAVES Longitudinal waves: vibrations parallel to wave direction rarefaction

6 WAVES Frequency, f: number of waves each second, unit: Hertz (Hz) 1 Hz = 1 wave/sec Period, T: time for one wave to pass, unit: s f=1/T Wavelength, : distance between identical points on two waves, unit: m

7 WAVES Amplitude, A: maximum displacement from equilibrium, unit: m Wave speed, v: speed of the wave, not the particles, unit: m/s v=f use difference in wave speeds to find distance ex: lightning & thunder

8 WAVE INTERACTIONS Reflection : waves "bounce back" at boundary

9 WAVE INTERACTIONS Law of Reflection:  i =  r i: incidence, r: reflection

10 WAVE INTERACTIONS Refraction: wave path bends as wave crosses boundary. Note that speed & wavelength change as wave moves into new medium, but frequency remains constant.

11 Refraction Examples 1. Dish filled with water 2. Light through glass

12 Refraction Rules When a wave goes from fast to slow mediums the wave will bend toward the normal. When a wave goes from slow to fast mediums the wave will bend away from the normal. V i Sin  r = V r Sin  i

13 WAVE INTERACTIONS Diffraction wave spreads out or “bends” beyond edge of barrier

14 WAVE INTERACTIONS Diffraction greatest when  is greater than or equal to the size of opening or object

15 SOUND INTERACTIONS Resonance (sympathetic vibration) objects have natural vibrating frequency sending waves to an object at at its natural frequency will make it vibrate pushing a child on a swing using microwaves to heat up water

16 SOUND WAVES Source: a vibrating object (vocal cord, string, reed, etc.)

17 SOUND INTERACTIONS

18 WAVE INTERACTIONS Interference: waves pass through each other without changing each other, but their displacements add together

19 WAVE INTERACTIONS constructive interference: combined wave displacement is greater than individual waves

20 WAVE INTERACTIONS destructive interference: combined wave displacement is less than individual waves

21 WAVE INTERACTIONS Standing Waves: interference of two identical waves going opposite directions makes waves appear to vibrate in place

22 WAVE INTERACTIONS Standing Waves: nodes: no displacement antinodes: maximum displacement Harmonic number is how many crests are trapped

23 SOUND WAVES Pitch: musical tone or note – frequency of a wave sonic spectrum: C major scale CDEFGABC frequency (Hz) musical scale: specific proportional frequencies

24 MUSICAL INSTRUMENTS =2L/n L: length of string, and n is 1,2,3… f=v/ v: wave speed in string v=√TL/m T: tension, m: mass of string

25 MUSICAL INSTRUMENTS Stringed Instruments quality: mixture of fundamental and harmonics (makes different instruments sound different) sound boards & boxes: more air surface contact - amplifiers

26 MUSICAL INSTRUMENTS

27 Wind Instruments pitch = frequency of vibration of column of air f = v/  v: sound speed in air = 340 m/s : wavelength, depends on length of air column

28 MUSICAL INSTRUMENTS open-end tube: each end of tube is antinode  = 2L/n L: length of tube and n is 1,2,3… Examples: flutes, saxophones, some organ pipes

29 MUSICAL INSTRUMENTS closed-end tube: closed end of tube is node =4L/n L: length of tube and n is 1,3,5 Examples: clarinets, some pipe organs

30 PHYSICS UNIT 5: VIBRATIONS, WAVES & SOUND

31 SOUND INTERACTIONS The Doppler Effect: apparent change in frequency due to motion of source or listener

32 SOUND INTERACTIONS Wave speed stays constant, remember wave speed depends on medium. Frequency changes and wavelength changes When source or observer moves toward each other wavelength decreases and frequency increases. When source or observer moves away from each other wavelength increases and frequency decreases

33 SOUND INTERACTIONS Radar: uses Doppler Effect in radio waves reflected off an object to determine its speed (speed traps, locating enemy aircraft) Red shift (decreased frequency) and Blue shift (increased frequency) of light tells astronomers whether a star or galaxy is moving toward or away from Earth.

34 SOUND INTERACTIONS

35 The Doppler Effect sound barrier: “pile-up” of sound waves (pressure) in front of object traveling Mach 1 sonic boom: cone-shaped pressure pulse following an object traveling at supersonic speeds (bow wave, also called water wake, following a speedboat)

36 SOUND INTERACTIONS

37 PHYSICS UNIT 5: VIBRATIONS, WAVES & SOUND

38 QUIZ 5.4 The speed of sound in earth is 3500 m/s. An earthquake wave, frequency 5 Hz, travels from its source to a distant mountain range and returns in 3.4 minutes. (a) How far away is the mountain range? (b) What is the wavelength of the earthquake wave? (c) If the mountain range was moving away at 0.50 m/s. what would be the frequency of the reflected wave? 357,000 m 700 m 5.00 Hz

39 UNIT 5 REVIEW f = 1/T v = f  i =  r v i sin  r = v r sin  i node dist = /2 loop height = 4A v = T I = P/4  r 2  = 10log( I / I 0 ) I 0 = 1× W/m 2 open pipe = 2L closed pipe = 4L x = vt


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