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Wave Motion ( 波動 )

Wave Motion ( 波動 ). Wave motion is a kind of vibration(oscillation), through which, energy (not matter) can be transferred from one place to other places. Vibration of water molecules perpendicular to wave(energy) travelling direction. Why can ocean waves lift a ship?.

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Wave Motion ( 波動 )

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  1. Wave Motion (波動) Wave motion is a kind of vibration(oscillation), through which, energy (not matter) can be transferred from one place to other places.

  2. Vibration of water molecules perpendicular to wave(energy) travelling direction.

  3. Why can ocean waves lift a ship? Waves carry energy

  4. Tsunamis carry a huge amount of energy

  5. 2 natures of wave . • Can travel through vacuum called EM(electromagnetic)waves. • Travel through medium called mechanical waves. e.g of EM waves: Radio wave Microwave Infrared radiation Visible light Ultraviolet radiation X rays Gamma rays Cosmic rays e.g. of mechanical waves: Sound wave Water wave Vibrating string Vibrating spring

  6. 2 types of wave vibration transverse wave(横波)、 longitudinal wave(縱波) 1.transverse wave: vibration is perpendicular to wave (energy) traveling direction Simulation of transverse wave: CH 10

  7. Some e.g. light vibration of particles

  8. Light(a kind of electromagnet wave(電磁波)is a transverse wave • Vibration of electric field & magnetic field • Electric field & magnetic field is a kind of energy. • Light is a form of energy.

  9. 2. Longitudinal wave: vibration is parallel to wave traveling direction. rarefaction Compression Simulation of longitudinal wave: CH 10

  10. Sound • Sound is a longitudinal wave. • Sound cannot travel through a vacuum . • Through air, sound waves travel at 330 m/s. • Sound waves move faster through solid and liquid than through gases. • Audiable frequency: 20 –20000 Hz • f > 20000 Hz called ultrasonic wave • Ultrasonic wave is used to detect flaws in metal pipe; to locate shoals of fish; to examine an unborn baby & as cleaners. • The quietest sound = 0 dB (decibels, unit of sound intensity) • Person talking = 60 dB • annoying sounds > 100 dB • Threshold of feeling = 120 dB

  11. To prove that sound is a longitudinal wave.

  12. Amplitude: maximum displacement of particles from equilibrium position. • 2. The bigger the amplitude, the greater the energy transferred Simulation: CH 10

  13. Frequency (f/Hz): number of vibrations in 1 second (Note: f always keeps constant) Wavelength(λ/m): distance between 2 consecutive particles that are in phase (distance between 2 crests/compression or 2 troughs/rarefaction) Simulation : CH 10

  14. Wave (energy) traveling speed(ms-1): • V = f λ • Sound speed in solid > in liquid > in gas • Water wave travels faster(slower) in deeper(shallower) region Period (T/s): Time for 1 vibration T = 1/f

  15. 2006 V = f λ=(2)(100) = 200 ms-1 (= 720 km h-1) V = distance/ time t = 1500/720 = 2 hours

  16. Phase (相位 )。 In phase(同相) : vibrations that are in steps anti- phase(反相): vibrations that are exactly opposite to each other. Wavelength: Distance between 2 consecutive particles that are in phase = λ Simulation: CH 10 transverse wave

  17. 12.5 cm 37.5 cm at rest • The above diagram shows the shape of a slinky spring at 0.5 s after the vibration is started, • Indicate the positions of compression (C) and rarefaction ( R ) . • Is the vibration started with a push or a pull？ • push • Find λ =？ • 37.5÷2.5 = 15 cm (Note: careful in choosing C & R) • Find the speed and frequency of the wave. • (37.5 + 12.5)÷0.5 = 100 cm/s • f = V ÷ λ = 100 ÷ 15 = 6.7 Hz

  18. 地震可按照震源深度分為淺源地震、中源地震和深源地震。淺源地震大多發生在地表以下30公里深度以上的範圍內，而深源地震最深的可以達到650公里左右。其中，淺源地震的發震頻率高，佔地震總數的70%以上地震可按照震源深度分為淺源地震、中源地震和深源地震。淺源地震大多發生在地表以下30公里深度以上的範圍內，而深源地震最深的可以達到650公里左右。其中，淺源地震的發震頻率高，佔地震總數的70%以上

  19. If MRichter magnitude scale (黎克特制)is increased by 1, E ( 能量)is magnified by a factor of 101.5 (=~32). In other words, the seismic (地震)energy of a M=6 earthquake is about 32 times as large as that of an earthquake M=5 earthquake, and is ~1000 ( =32x32= 1024)times that of an M=4 earthquake. Energy released by M = 8 is greater than that by M = 1 by : ( 32x32x32x32x32x32x32 = 34359738368 ~ 30000000000 ~ 300億倍能量 Earth's daily receipt of solar energy ~ M = 12

  20. Richter Effect Less than 3.5 not felt, but recorded. 3.5-5.4 Often felt, but rarely causes damage. Under 6.0 At most slight damage to well-designed buildings. Cause major damage to poorly constructed buildings over small regions. 6.1-6.9 Can be destructive in areas up to about 100 kilometers across where people live. 7.0-7.9 Major earthquake. Can cause serious damage over larger areas. 8 or greater Great earthquake. Cause serious damage in areas several hundred kilometers across.

  21. M = 10 : As if a 2 km rocky meteorite impacting to our earth at 90,000 km/h Never recorded The largest recorded earthquake was the Great Chilean Earthquake of May 22, 1960 which had a magnitude of 9.5

  22. e.g 1 If the speed of a wave on water surface is 8 m/s and theλis 80m 。Find the time between the arrival of 2 successive waves？ 10 s • e.g 2 • If the frequency of a wave is 10Hz and λ = 33 m。 • Find the wave speed = ？ • 330 m/s • If the frequency is doubled, find the new λ =？ • 16.5 m

  23. Period週期(T/s) Time for 1 complete vibration。 T = 1/ f or: Time for wave to travel 1λ. t=0 t=1T t=2T

  24. eg The following diagram shows a transverse wave traveling from left to right , If each particle can finish 4 vibrations in 16 s: Q  T 2cm  R P    S 5cm • Find the amplitude • 5 cm • (b)find the wave speed • 0.02 m/s • (c) Sketch the shape of the diagram after half a period.

  25. Displacement from equilibrium position

  26. 四川汶川發生黎克特制7.8級地震，威力相當於二百五十六顆原子彈，震動大半個中國，遠至港澳台、泰國、越南都有震感。死亡人數已增加至萬人四川汶川發生黎克特制7.8級地震，威力相當於二百五十六顆原子彈，震動大半個中國，遠至港澳台、泰國、越南都有震感。死亡人數已增加至萬人 中國地震局地震預測研究所研究員張國民稱，汶川發生地震是屬於淺源地震(約10公里)，破壞力度較大。

  27. Describing waves with graphs: • Displacement – distance graph of a wave • Displacement – time graph of a wave

  28. Displacement – distance graph of a wave • shows the displacements (y-axis) of particles at various positions (x-axis) of a wave from their equilibrium position at a particular time, it can show the amplitude and wavelength of the wave. Displacement/m + Position/m - P.23

  29. 1 0 8 6 2 4 –1 Use displacement – distance graph to determine the motion of particles present displacement / cm direction of travel Q P distance / cm R S later P :moving downwards Q :momentarily at rest. Traveling direction must be given R :moving upwards S :momentarily at rest.

  30. The diagram below shows the displacement - distance graph for a transverse wave with amplitude 1.0 cm moving to the right at 8 cm s-1. + -

  31. 2. Displacement – time graph of a wave shows the displacement (y-axis) of a particular particle from its equilibrium position with time (x-axis), it shows only amplitude and period(or frequency) of the wave. The displacement - time graph for particle 13 is shown below. 1 period

  32. Traveling longitudinal wave (P.23): Traveling direction must be given

  33. Displacement-distance graph of longitudinal waves(P.27): The Displacement-distance graph of longitudinal waves looks like a transverse wave!

  34. Class work: P.33 Questions: 1-8 HW: P.34 7,8,9,10,11

  35. 1 0 –1 2. Displacement – timegraph of a wave Shows the displacements (y-axis) of a particular particle at various time (x-axis) of a wave from its equilibrium position, it can show the amplitudefrequency and period of the wave. displacement / cm amplitude Time/s T 2T period

  36. P.27 4. P.28 4,5,6,7

  37. P.35 1990

  38. P.35 1998

  39. P.35 2002

  40. O I L N E B F A C D G H J K M                O G N A J M D I L C E B K                F H A longitudinal wave is traveling to the right, some of the the medium particles are recorded as: At time = 0 At time = t 5 cm Take the displacement to the right as positive. Sketch the displacement-distance graph of the wave.

  41. displacement / cm 6 Time = t distance J G A M D 3 s later 6 Answer: If the frequency of the wave is 0.5 Hz, on the displacement-distance above, sketch the displacement-distance graph of the wave (from coil A to coil O) 3 s later

  42. displacement / cm travelling direction A  4 D  distance / cm B C  0  10 20 15 5 4 A transverse wave is traveling to the right shown: • At the instant shown, which of the particles A, B, C or D,is/are • momentarily at rest, • A • moving upwards, and • B, • moving downwards? • C, D If particle Bperforms 5 complete oscillations in 2 s , Sketch the displacement-time graph of particle A from t = 0 s to t = 0.4 s.

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