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Waves. Definition of wave – A disturbance that transfers energy through matter or space – “Disturbance”-a change from a normal state.

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Presentation on theme: "Waves. Definition of wave – A disturbance that transfers energy through matter or space – “Disturbance”-a change from a normal state."— Presentation transcript:

1 Waves

2 Definition of wave – A disturbance that transfers energy through matter or space – “Disturbance”-a change from a normal state

3 Periodic or Harmonic Motion Motion that repeats itself in the same amount of time cycle One repetition of motion called a cycle Examples? What does graph look like?

4 period (T) Amount of time to complete cycle called a period (T) Frequency (f) Frequency (f) is how many complete cycles occur in one second T = 1/f or f =1/T T = 1/f or f =1/T Amplitude Amplitude is the amount of displacement from rest Periodic or Harmonic Motion

5 Graphing harmonic motion

6 Graphing Harmonic Motion

7 Homework Complete Harmonic Motion Worksheet

8 Waves demonstrate harmonic motion Wave movement through matter – Particles move – Particles return to original position (location)

9 Types of Waves Based on particle motion in wave 2 types 1. Transverse 2. Longitudinal

10 Wave Type-Transverse Particle motion perpendicular to wave direction d.wikimedia.org/wikipedia/commons/6/6d/Onde_cisaillement_impulsion_1d_30_petit.gif

11 Wave Type-Transverse Particle motion perpendicular to wave direction

12 Parts of a Transverse Wave

13 Examples of Transverse Waves Shaking a string Ocean waves Ripples on a pond “Stadium” or human wave Electromagnetic (radio, light, micro ect…)

14 Wave Type-Longitudinal Particle motion in direction of wave

15 Wave Type-Longitudinal Particle motion in direction of wave

16 Parts of a Longitudinal Wave Particle motion in direction of wave

17 Examples of Longitudinal Waves Sound waves Oscillating springs

18 Sound waves are longitudinal waves

19 Represent longitudinal waves as transverse waves Particle displacement in a longitudinal wave can be graphed as a transverse wave – Particle motion from rest graphed as amplitude os/StandingWaves/Flash/long_wave.html

20 Sound Waves Sound waves move vibrational energy through matter Sound waves are longitudinal waves

21 Wave Properties Common Characteristics of Wave – Length – Height – Frequency (how often they occur) Period (how long to make 1 cycle) – Speed All Characteristics of Waves Can Vary

22 Wave Characteristics Wavelength (λ)-the distance between repeating parts of a wave – Trough to trough – Peak to Peak – Rarefaction to Rarefaction – Compression to compression -Or any other repeating part

23 Wave Characteristics Wave amplitude (height)-the maximum displacement from the undisturbed position of the medium to the top of a crest or bottom of a trough

24 Check Your Understanding Transverse Waves The wavelength of the wave in the diagram above is given by letter ______. The amplitude of the wave in the diagram above is given by letter _____.

25 Check Your Understanding Transverse Waves Indicate the interval which represents one full wavelength.

26 Wave Characteristics The frequency (f) of a wave is the number of complete waves (cycles) that pass the observer in a given time. Hertz is the unit of frequency, and just means how many cycles (peaks) per second.

27 Wave Characteristics The period (T) of a wave is the time for a wave to make one complete cycle (peak to peak). The period is related to the frequency by the following equation f=1/T

28 Wave Characteristics The speed (v) of a wave is the how fast the wave is moving – distance the wave travels in a certain amount of time.

29 Wave Characteristics The relationship between the speed, frequency, period and wavelength Example: – 2 waves each second (i.e. frequency = 2 Hz)frequency – the period is equal to 1/f = ½ second – the distance between the waves as 25 cm: this is the wavelength. wavelength In 0.5 s, waves move 25 cm, so we can find the speed using: speed= v = λ x f = 25 x 2 = 50 cm/sec OR speed = v = λ x 1/T = 25 x (1÷ ½) = 50 cm/sec

30 Homework Complete Wave Worksheet

31 Factors Affecting the Speed of Sound Sound waves require matter to travel – No particles to compress = no waves = no sound Speed of sound depends on matter or medium – Speed does not depend of the source Factors that affect the speed of sound include: – Temperature of medium – Elasticity of medium – Density of medium

32 Speed of Sound Temperature Affects – Temperature changes affect sound speed more in gases than solids or liquids Particles spaced apart in gases Temperature affects spacing of particles in gases (Charles & Boyles Gas Laws) Temperature – High temperature air = higher sound speed – Low temperature air = lower sound speed – Heat and sound = kinetic energy

33 Speed of Sound Elasticity – Elasticity = The tendency of an object to return to its original shape once the forces are no longer applied. – Phases of matter have great effect on elasticity of matter – Greater elasticity = Greater speed of sound – v solids > v liquids > v gases

34 Speed of Sound Density – Less effect on speed of sound than elasticity – Within a single phase of matter = greater impact – Density = mass/volume – Within a single phase of matter Greater density = lower speed of sound Mass of heavier particles are harder to move Greater density = Greater inertia

35 Speed of Sound Materials – The speed of sound varies through different materials MaterialSpeed of Sound (m/s) Iron5890 Lead1960 Water1479 Ice3980 Air330

36 Sonic Boom When an object travels faster than the speed of sound it breaks the “sound barrier” Waves all traveling at same speed, pile up on each other as plane pushes them together Result is a “sonic boom”

37 Properties of Sound Intensity-measure of sound’s amplitude – Related to loudness, but loudness is subjective Intensity measured in decibels (dB) Increase in 10 dB results in sound that is twice as loud SourceIntensity Level (dB) Threshold of hearing (TOH)0 Rustling leaves10 Whisper20 Normal conversation60 Busy street traffic70 Vacuum cleaner80 Rock concert110 Threshold of pain130 Military jet takeoff140 Eardrum perforation160

38 Properties of Sound Frequency and Pitch – Frequency is number of waves in a certain amount of time – Frequency is measured in Hertz (Hz) – Pitch is related to frequency, describes how high or low the sound is. Pitch is subjective. – Pitch is the sensation of frequencies High frequency = high pitched sounds Low frequency = low pitched sounds

39 Human Hearing and Frequency Humans can hear frequencies ranging from 20-20,000 Hz Ultrasound are sound waves with frequencies above the human hearing range

40 Properties of Sound Sound Quality is referred to Timbre Differences in timbre allow listeners to hear not only the difference between an oboe and a flute, but also the difference between two different flutes, even if both flutes are playing notes at the same frequency and amplitude

41 Properties of Sound Descriptions related to timbre – Reedy – Brassy – Clear – Rounded – Piercing – Strident – Harsh – Warm – Mellow – Resonant – Dark or Bright – Heavy or Light – Flat – Having much, little, or no vibrato

42 Properties of Sound Doppler Effect The observed effect between an observer and a sound source when one is moving relative to another – distance decreasing → perceived frequency (pitch) is increased – distance increasing → perceived frequency (pitch) is decreased

43 Doppler Effect Examples – capa.org/~mmp/applist/doppler/d.htm capa.org/~mmp/applist/doppler/d.htm (visual) – _stuff/flashlets/doppler.htm _stuff/flashlets/doppler.htm (visual and audio)

44 Wave Interactions What is the result of collisions between waves and other waves or objects? – Waves transfer energy – Collisions results in energy transfer Lose or gain energy

45 Wave Interactions Wave colliding with other waves cause interference – Principle of Superposition Waves add (subtract) amplitudes (energy) – Two kinds of interference Constructive (add) Destructive (subtract)

46 Sound Wave Interactions Interference – Constructive = increase in intensity – Destructive = decrease in intensity

47 Wave Interactions Constructive Interference – waves add to produce a new wave with larger peaks than either of the two original waves

48 Wave Interactions Constructive interference

49 Wave Interactions Destructive Interference – waves add to produce a new wave with smaller peaks than either of the two original waves

50 Sound Wave Interactions Interference

51 Phase shifts of waves The phase shift tells an observer how out of sync two or more waves are – It gives the offset of the two waves In phase = constructive interference Out of phase = destructive interference

52 In phase and out of phase waves Waves are completely out of phase – destructive interference Waves are completely in phase – constructive interference

53 Sonic Boom Constructive interference of waves = sonic boom Crack of a bull whip = sonic boom

54 Standing waves on a string

55 Harmonics of Standing Waves

56 Harmonics of standing waves

57 Homework Complete Sound and Standing Waves Worksheets

58 Sound Wave Interactions Resonance – Is the vibration of an object at its natural frequency This frequency depends on the length of the object

59 Sound Wave Interactions Resonance – Tuning forks and bells vibrate at their natural frequency All objects have a frequency that they resonate at – When waves bounce back and forth on themselves within the object and constructively interfere, we call it resonance.

60 Sound Wave Interactions Resonance Examples waves/standing_wave2.html waves/standing_wave2.html arrows_Bridge_destruction.ogg (Movie of Tacoma Narrows Bridge) arrows_Bridge_destruction.ogg

61 Wave Interactions Wave colliding with objects have following 3 outcomes 1. Refraction 2. Reflection 3. Diffraction

62 Wave Interactions REFLECTION – Reflection is when waves bounce from a surface back toward the source. – A mirror reflects the image of the observer. – None of the characteristics of a wave are changed by reflection. – No change-wavelength, frequency, period – Change-wave direction

63 Wave Interactions REFLECTION – Law of Reflection – Angle of Incidence = Angle of Reflection

64 Sound Wave Interactions Reflection – When a sound wave in air reaches the surface of another material, some of the sound is reflected off the surface and some passes into the material (transmitted)

65 Sound Wave Interactions Reflection – Smooth surfaces best more sound will be reflected from a smooth wall made of mud than a pile of dirt reason is that the rough or porous surface allows for many reflections, resulting in more absorption and less reflection

66 Sound Wave Interactions Reflections – Echoes When sound reflects off a smooth flat surface, an echo or reproduction of the sound can be heard. Echoes are more noticeable if the surface is far enough away to allow for a time-lag between when the sound is made and when it is hear. (~0.1 seconds)

67 Echo Problem If the speed of sound in air is 340 m/sec and you hear an echo 1 sec after you yell, how far away is the reflector? Remember that that the sound wave has to travel there and back so V=total distance/time 340m/sec= total distance/1 sec Total distance = 340 m/sec x 1 sec = 340 m Distance to reflector = total distance ÷ 2 = 170 m

68 Wave Interactions DIFFRACTION – Diffraction is the bending of waves when they collide with the edges of objects. – All waves diffract. – We can hear around a corner because of the diffraction of sound waves.

69 Sound Wave Interactions Diffraction – Because sound waves diffract, you can hear around corners and from behind obstacles

70 Wave Interactions REFRACTION – Refraction is when waves are deflected when passing from one medium to another – The wave generally changes direction.

71 Sound Wave Interactions Refraction is the bending of waves when they enter a medium where their speed is different.

72 Sound Wave Interactions Refraction-Effect – Cool air-lower speed, Warm air-higher speed Normally, only the direct sound is received. But refraction can add some additional sound, effectively amplifying the sound. Natural amplifiers can occur over cool lakes.

73 Homework Complete Wave Interactions Worksheet

74 The End


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