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Waves, Optics

Waves, Optics. Waves, Vibrations, Frequency. Waves, Vibrations, Frequency. Where have you seen waves before?. Sound sensation  produced by stimulation of the organs of hearing by vibrations transmitted through the air or other medium. Objectives. Describe what a wave is

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Waves, Optics

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  1. Waves, Optics Waves, Vibrations, Frequency

  2. Waves, Vibrations, Frequency • Where have you seen waves before?

  3. Sound sensation produced by stimulation of the organs of hearing by vibrations transmitted through the air or other medium.

  4. Objectives • Describe what a wave is • Know where waves come from • Name and describe features of the two main wave types (transverse and longitudinal) • Note the different types of waves • Be able to calculate Frequency and Period of a vibration

  5. If you scream in space does it make a sound? • If a tree falls in the forest and no one is there, does it make a sound?

  6. Waves • Waves transfer energy from one place to another through a medium • Although the waves (and thus the energy) is moving the medium does not

  7. Waves Waves travel in 2 ways: 1. Transverse: • Black = Wave direction • Red = Particle direction • Wave direction is perpendicular to particle direction • Deep ocean wave, guitar string

  8. Waves Waves travel in 2 ways: 2. Longitudinal: • Black = Wave direction • Red = Particle direction • Wave direction is parallel to particle direction • Sound, deep earthquake

  9. Waves Wave Types: • Mechanical (through media) • Ocean waves • Sound Waves • Flapping Flag • Electromagnetic (through space) • Light • X-ray • Ultraviolet • Infrared • Radio waves • Microwaves

  10. Waves http://www.youtube.com/watch?v=nFzu6CNtqec

  11. Waves Surface Waves: • When a water wave is near the surface we get both Longitudinal and Transverse waves together

  12. Measuring Vibrations • All waves are caused by vibrations • Frequency = vibrations / second • Frequency = cycles / second • measured in Hertz (Hz) • Period = time it takes to Complete a cycle (s) • 1 Hz = 1 cycle / second

  13. Equations F= frequency Λ = wavelength V= velocity T= period V= f * λ T=1/f The period is inversly proportional to the freqency

  14. 1. Compare and contrast a transverse wave and on longitudinal wave. • 2. 4 waves past by in 2 seconds that have a wavelength of 3 meters, find the • A. frequecy • B. period • C. velocity

  15. Oscillatory system – uses simple harmonic motion – back and forth motion

  16. Cycle • 1 cycle = the time it takes to go from here • To here • And then back again

  17. PendulumCycleFormingA Wave

  18. Cycle

  19. Frequency • HSBC Pendulum

  20. Period • Period is the amount of time for a single vibration to occur. • Period = 1/frequency • Period is measured in seconds

  21. Pendulum lab • Inquiry lab • What affects the period of a pendulum? • How could you measure the period?

  22. 4/24 • 1. What variable are you testing in your pendulum experiment? • 2. A pendulum swings back and forth 47 times in 60 seconds. a. What is its period? b. What is its frequency?

  23. 1. A boat bobs up and down 20 times every minute, what is its frequency? • 2. What is the boat’s period?

  24. Practice Questions 1. A boat bobs up and down 20 times every minute, what is its frequency? • f = cycles / time = 20 / 60s = 0.3Hz 2. What is the boat’s period? • t = 1 / f = 1 / 0.33Hz = 3s

  25. 1. What variable are you testing in your pendulum experiment? • 2. Create a diagram of a pendulum showing when it reaches maximum potential energy and maximum kinetic energy

  26. 4/25 • Describe your findings in the pendulum lab. What is the relationship between frequency and period? • Today: Report your finding to classmates. These should include claim, evidence (data table and graphs) and reasoning.

  27. What is your grade in the class? • Are you missing any assignments? If so which ones?

  28. Summary • A wave transfers energy through a medium • Waves originate from a vibrating source • Frequency (Hz) = cycles / time (s) • Period (s) = 1 / Frequency (Hz) • Transverse waves – Wave direction is perpendicular (ḻ) to particle direction • Longitudinal waves – Wave direction is parallel (ǁ) to particle direction

  29. What does the period of a pendulum depend on? • What happens when you ring two notes of different frequency?

  30. Warm up see hand out • Explain why you hear a beat when you hit two tuning forks of slightly different frequency

  31. 4/29 • The speed of sound is 350 m/s. How far away is lightning if you see the lightning then hear it 3 seconds later? • Why are some things louder?

  32. Pitch – apparent frequency we hear • Below 20 hertz – infrasonic • Above 20,000 hertz -

  33. 26.5Loudness Amplitude – amount of energy in a wave

  34. 26.5Loudness

  35. 26.5Loudness • Starting with zero at the threshold normal hearing, an increase of each 10 dB means that sound intensity increases by a factor of 10. • A sound of 10 dB is 10 times as intense as sound of 0 dB. • 20 dB is not twice but 10 times as intense as 10 dB, or 100 times as intense as the threshold of hearing. • A 60-dB sound is 100 times as intense as a 40-dB sound.

  36. 26.2Sound in Air Clap your hands and you produce a sound pulse that goes out in all directions. Each particle moves back and forth along the direction of motion of the expanding wave.

  37. 1. A sound wave is a pressure wave; regions of high (compressions) and low pressure (rarefactions) are established as the result of the vibrations of the sound source. These compressions and rarefactions result because sound • a. is more dense than air and thus has more inertia, causing the bunching up of sound. • b. waves have a speed which is dependent only upon the properties of the medium. • c. is like all waves; it is able to bend into the regions of space behind obstacles. • d. is able to reflect off fixed ends and interfere with incident waves • e. vibrates longitudinally; the longitudinal movement of air produces pressure fluctuations

  38. Since the particles of the medium vibrate in a longitudinal fashion, compressions and rarefactions are created Compression – high pressure Rarefaction – low pressure

  39. 26.2Sound in Air • Opening and closing a door produces compressions and rarefactions. • When the door is opened, a compression travels across the room. • When the door is closed, a rarefaction travels across the room.

  40. 26.1The Origin of Sound All sounds originate in the vibrations of material objects.

  41. Doppler effect • http://www.loncapa.org/~mmp/applist/doppler/d.htm

  42. 26.3Media That Transmit Sound Most sounds you hear are transmitted through the air. Put your ear to a metal fence and have a friend tap it far away. Sound is transmitted louder and faster by the metal than by the air. Click two rocks together underwater while your ear is submerged. You’ll hear the clicking sound very clearly. Solids and liquids are generally good conductors of sound.

  43. 26.4Speed of Sound The speed of sound in a gas depends on the temperature of the gas and the mass of the particles in the gas. The speed of sound in a material depends on the material’s elasticity.

  44. 26.4Speed of Sound The speed of sound in dry air at 0°C is about 330 meters per second, or about 1200 kilometers per hour. This is about one-millionth the speed of light. Increased temperatures increase this speed slightly—faster-moving molecules bump into each other more often. For each degree increase in air temperature above 0°C, the speed of sound in air increases by about 0.60 m/s.

  45. 26.4Speed of Sound • The speed of sound in a solid material depends not on the material’s density, but on its elasticity. Elasticity is the ability of a material to change shape in response to an applied force, and then resume its initial shape. • Steel is very elastic. • Putty is inelastic. • Sound travels about 15 times faster in steel than in air, and about four times faster in water than in air.

  46. 26.8Resonance Resonance occurs whenever successive impulses are applied to a vibrating object in rhythm with its natural frequency. The Tacoma Narrows Bridge collapse was caused by resonance. Wind produced a force that resonated with the natural frequency of the bridge. Amplitude increased steadily over several hours until the bridge collapsed.

  47. Natural frequency - - natural frequency at which an object vibrate – springiness • Drop a wrench and a baseball bat on the floor, and you hear distinctly different sounds. • Objects vibrate differently when they strike the floor. • Resonance- increase in amplitude when a frequency of a vibration reaches the natural frequency

  48. 26.6Natural Frequency Drop a wrench and a baseball bat on the floor, and you hear distinctly different sounds. Objects vibrate differently when they strike the floor. We speak of an object’s natural frequency, the frequency at which an object vibrates when it is disturbed.

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