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Waves

Waves. Unit 8 Chapter 11. Topics to be covered in this unit. 1. Types of Waves. 2. Characteristics of Waves. 3. Wave Interactions. What is a wave?. Waves are disturbances that transmit energy through matter or space.

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Waves

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  1. Waves Unit 8 Chapter 11

  2. Topics to be covered in this unit 1. Types of Waves 2. Characteristics of Waves 3. Wave Interactions

  3. What is a wave? • Waves are disturbances that transmit energy through matter or space. • Example – when you throw a stone into a pond… it creates a ripple on the surface of the water.

  4. How waves travel • Ripples in the pond • Sound traveling through air • Earthquakes in the ground • These are all examples of mediums in which waves can travel. • A medium is the matter through which a wave travels.

  5. How waves travel • Waves that require a medium are called mechanical waves. • Almost all waves require a medium • Exceptions are electromagnetic waves

  6. Electromagnetic wave • Electromagnetic wave is a wave caused by a disturbance in electric and magnetic fields and does not require a medium.

  7. Light • Light can travel from the sun to the Earth through the empty space between the two. • Light does not need a medium • Light waves consist of changing electric and magnetic fields in space. • They are also called electromagnetic waves • Examples: visible light and radio waves

  8. Waves transfer energy • Remember – energy is the ability to do work. • Waves carry energy because they can do work. • Water waves can move a boat or leaf • Sound waves impact your eardrum • Light waves work on your eye • The bigger the wave, the more energy it carries.

  9. Tsunami in Japan

  10. Waves transfer energy • Tsumani waves carry enough energy to cause a lot of damage to coastal towns and shorelines. • Normal-size waves do work on the shore to break up rocks into tiny pieces forming sandy beaches.

  11. Energy may spread out as a wave travels • The closer you are to speakers, the louder the music. • Waves spread out in circles that get bigger as the waves move farther from the center. • Each circle (called a wave front) has the same amount of total energy. But as the circle get larger, the energy spreads out over a larger area.

  12. Vibrations and Waves • Waves are related to vibrations • Example: a singer sings (vocal cords move back and forth) creating sound. The sound waves reach your ears causing your eardrum to vibrate. This vibration is interpreted by your brain as sounds. • Most waves are caused by a vibrating object • Electromagnetic waves may be caused by vibrating charged particles • In a mechanical wave, the particles in the medium also vibrate as the wave passes through the medium.

  13. Vibrations involve transformations of energy • Vibration: in a general sense, anything that switches back and forth, to and from, side to side, in and out, off and on, loud and soft, or up and down is vibrating. A vibration is a wiggle in time. • Wave: a wiggle in both space and time is a wave. A wave extends from one place to another.

  14. Vibrations involve transformations of energy • Vibrations and waves: the source of all waves is something that is vibrating. Waves are propagations of vibrations throughout space. • Example is a pendulum in a clock.

  15. simple harmonic motion is a type of motion where the restoring force is directly proportional to the displacement

  16. Simple Harmonic Motion • A wave whose source vibrates with simple harmonic motion is called a sine wave • As the mass moves down, the spring is exerting force which pushes it back to the original position. This will allow the mass to keep bouncing up and down forever.

  17. Damped Harmonic Motion • Unlike the simple harmonic motion which will continue forever. The damped harmonic motion will transfer its energy to the second mass, it slows down and then returns to its resting position. • http://www.animations.physics.unsw.edu.au/jw/oscillations.htm#Damped

  18. Wave Types Transverse waves vibrate across from direction of travel Longitudinal waves vibrate along the direction of travel (as in a spring)

  19. Longitudinal Wave • The wave we see here is a longitudinal wave. • In a longitudinal wave, the medium particles vibrate parallel to the motion of the pulse. • This is the same type of wave that we use to transfer sound.

  20. Transverse waves • A second type of wave is a transverse wave. • We said in a longitudinal wave the pulse travels in a direction parallel to the disturbance. • In a transverse wave the pulse travels perpendicular to the disturbance.

  21. What’s the difference? • The differences between the two can be seen

  22. Surface Wave • Surface waves occur at the boundary between two different mediums such as between water and air. • Example: The waves on the ocean are not simply transverse or longitudinal waves.

  23. Characteristics of Waves • Waves can be observed with many different properties: • Large or small • Close together or very far apart • However, they can all be described with their properties using a sine curve.

  24. Wave PropertiesWavelength Wavelength, l, is the distance between any two successive identifical parts of a wave.

  25. Wave PropertiesAmplitude Amplitude is the greatest distance that particles in a medium move from their normal position when a wave passes.

  26. Parts of a Wave • Crest: The highest point of a transverse wave

  27. Parts of a Wave • Trough: The lowest point of a transverse wave. • These are the points where the wave exhibits its maximum negative or downward displacement.

  28. Longitudinal wave parts: • Compressions- a region in a longitudinal wave where the particles are closest together. It is an area of high density • Rarefactions- A decrease in density and pressure in a medium.

  29. Wave PropertiesPeriod The wave period, P, the time required for one full wavelength to pass a certain point.

  30. Wave PropertiesFrequency Frequency, f, is the number of vibrations that occur in a 1 second time interval.

  31. Frequency-Period Equation • The frequency and period of a wave are related. • If more vibrations are made in a second, each one takes a shorter amount of time. • The frequency is inverse of the period. • SI unit is Hertz (Hz) Frequency = 1 period f = 1/T

  32. Visible Light • Our eyes can detect light with frequencies from 4.3 x 1014 Hz to 7.5 x 1014 Hz. • This is called the visible light

  33. Electromagnetic Spectrum • Light occurs at other ranges we cannot see with our eyes. • The full range is called the electromagnetic spectrum.

  34. Wave speed • Wave speed is the speed at which a wave passes through a medium. • Formula: Wave speed = frequency x wavelength v = f x  SI unit for wave speed is meters per second. m/s

  35. Practice problem • The average wavelength in a series of ocean waves is 15.0 m. A wave arrives on average every 10.0 s, so the frequency is 0.100 Hz. What is the average speed of the waves? • v = f x 

  36. Practice problem • The average wavelength in a series of ocean waves is 15.0 m. A wave arrives on average every 10.0 s, so the frequency is 0.100 Hz. What is the average speed of the waves? v = f x  = 0.100 Hz x 15.0 m = 1.5 m/s

  37. Doppler Effect • Doppler effect is an observed change in the frequency of a wave when the source or observer is moving. • Pitch of a sound, how high or low it is, is determined by the frequency at which sound waves strike the eardrum in your ear.

  38. Red shift?

  39. Expand that….. • Wrap your mind around this

  40. Of course….. • There's this take on it

  41. Sound Waves Molecules in the air vibrate about some average position creating the compressions and rarefactions. We call the frequency of sound the pitch.

  42. Doppler Effect • Refers to the change in frequency when there is relative motion between an observer of waves and the source of the waves • Doppler with Sound

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