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Waves and Energy


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Waves and Energy

  1. 1. Waves & Energy Powerpoint Templates
  2. 2. Waves are a Form of Energy• What do we know about energy? – It is the ability to do work (make changes) – It cannot be created or destroyed – It can be transferred between objects• Waves are vibrations that transfer energy from place to place – back-and-forth movements • push-and-pull forces • "disturbance" or oscillation – spread in all directions Powerpoint Templates
  3. 3. Mechanical vs. Electromagnetic• Mechanical Waves – travel ONLY through matter • energy is transferred from place to place • matter moves but returns to original location – travel through a solid, liquid or gas medium • type of medium affects how quickly the wave can travel – cannot travel through space where there is no matter – Examples: • sound waves • ocean waves • seismic waves Powerpoint Templates
  4. 4. Mechanical vs. Electromagnetic• Electromagnetic Waves – CAN travel through a vacuum (lack of matter, even air molecules) – can also travel through matter (solid/liquid/gas)• Electromagnetic Spectrum – radio waves, microwaves, infrared waves – X rays, light, heat • well look at these in a couple weeks Powerpoint Templates
  5. 5. Anatomy of a Wave• Crest: highest point on a wave• Trough: lowest point Amplitude on a wave Node• Node: midway point between crest & trough• Wavelength: distance between crests (λ in meters)• Amplitude: height of the wave (A) - (MIDDLE to crest) – shows how much energy a wave carries• Frequency: how many waves hit a certain point every second (Hz = Hertz = waves per second) Powerpoint Templates
  6. 6. Transverse Waves• A transverse wave has vibrations (oscillations) perpendicular to the direction the wave travels – propagation (direction wave travels) is to the right – oscillation is up and down• May be mechanical or electromagnetic – Examples: ocean waves, X-rays or light If the graph show here represented 1 second of time, what would the Oscillation frequency be? Answer: 2.5 Hz Powerpoint Templates
  7. 7. Longitudinal Waves• A longitudinal wave oscillates parallel to the direction the wave travels – propagation is to the right – oscillation is left and right• All longitudinal waves are mechanical – Examples: sound waves, seismic waves• Also called compressional waves If the graph show here represented 1 second of time, what would the frequency be? Answer: 3 Hz Powerpoint Templates Oscillation
  8. 8. Longitudinal Waves• In longitudinal waves, matter is compressed (squeezed or pushed together) to form the wave motion. – point of greatest compression = "crest" – point coils are most spread out (rarefaction) = "trough"• Amplitude is displayed in how tightly the medium is squeezed together in its regions of compression. – more tightly compressed coils Templatesamplitude (more energy) Powerpoint = higher
  9. 9. Sound Waves• When you hear a sound, it is caused by air molecules being compressed in waves. Powerpoint Templates
  10. 10. Transverse & Longitudinal Waves Rarefaction Comparison Powerpoint Templates
  11. 11. Powerpoint Templates
  12. 12. Wavelength & Frequency• Wavelength, frequency and wave speed can be described mathematically by the following equation: wave speed (v) = frequency (f) x wavelength (λ) f = v λ Powerpoint Templates
  13. 13. A, f & λ Relationships• Beads on a String Demo f= v λ• As frequency increases, the wavelength decreases. – f and λ are inversely proportional Powerpoint Templates
  14. 14. Practice Problem• A marine weather station detects waves which are 9.28 meters apart and 1.65 meters high and travel a distance of 50 meters in 21.8 seconds. Determine the speed, amplitude and frequency of these waves. Speed Speed (v) = distance/time = 50m ÷ 21.8s = 2.3m/s Amplitude Amplitude (A) = ½ wave height = .5 x 1.65m = .825m Frequency Frequency (f) = v/λ = 2.3m/s ÷ 9.28m = .25 Hz Powerpoint Templates
  15. 15. Frequency & Period• The period (T) of a wave is the time it takes for one wave to pass a certain point (or the time between each wave).• If this graph shows 1 Period (T) second of time, the frequency (f) is 3Hz.• 3 waves per second means the period (time between each wave) is T=1 1/3 of a second. f Powerpoint Templates
  16. 16. Practice Problem• Strong winds can apply a significant enough force to tall skyscrapers to set them into a back-and-forth motion. The amplitudes of these motions are greater at the higher floors and barely observable for the lower floors. It is said that one can even observe the swaying motion of the Sears Tower in Chicago on a windy day. – As the Sears Tower vibrates back and forth, it makes about 8.6 vibrations in 60 seconds. Determine the frequency and the period of vibration of the Sears Tower. f = waves per second = ?/s T=1 f f = 8.6/60s = .143 = .14 Hz period = 1/f = 1 = 6.98s (about 7 seconds) .14 Powerpoint Templates