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Plan for Today (AP Physics I)

Plan for Today (AP Physics I). Lecture/notes on Waves. Waves. Motion of a disturbance Ex – jump Do you feel it? Do you hear it?. When I jump. Energy is transferred through the floor (vibrates) Energy is transferred through air (sound). Wave motion. Transmits energy (not particles)

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Plan for Today (AP Physics I)

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  1. Plan for Today (AP Physics I) • Lecture/notes on Waves

  2. Waves • Motion of a disturbance • Ex – jump • Do you feel it? • Do you hear it?

  3. When I jump. . . • Energy is transferred through the floor (vibrates) • Energy is transferred through air (sound)

  4. Wave motion • Transmits energy (not particles) • Part of the floor/air stayed in place

  5. Types of Waves • Mechanical • Require a medium • Types of mechanical waves: • E-M (electromagnetic) • Doesn’t require • Types of electromagnetic waves:

  6. Other classifications • Longitudinal • Vibration parallel to motion • Transverse • Vibration perpendicular to motion • Examples with slinky • Spring with ribbon attached • Shows motion of energy not particles • Sound – big longitudinal wave we will look at (next unit)

  7. Wave information • Laser disks 11-15

  8. Pictures of Waves • Picture of Height of water striking a dock

  9. Pictures of Waves • Picture of Height of water striking a dock • T = period (time to repeat) • Lambda = wavelength (distance) • A = amplitude

  10. Picture of Wave Continued • Looking out over a lake with waves on it

  11. Velocity of a Wave as a function of what? • Brain teaser • In WWII, a sailor dives off a ship about to explode. He swims under water until he hears the explosion, then he pops his head out of the water and hears another explosion • After he is rescued, others claim there was only 1 explosion. But he heard 2 – why?

  12. Speed of Sound • Air – 350 m/s • Water – 1100 m/s • Steel – 5000 m/s • Speed of sound is a function of the medium and the medium only

  13. Velocity of a wave is a function of the medium

  14. Why is there the velocity difference • Spacing of the molecules • Air • Motion has to travel all the way over • Water • Steel

  15. How fast does an air molecule vibrate? • Around 350 m/s

  16. Formula • v = x/t • But since wavelength () is a distance and T is a time. . . • v = / T • v = * f

  17. Example Problems • A tuning fork produces a sound with a frequency of 256 Hz and a wavelength in air of 1.35 m. • What value does this give for the speed of sound in air? • What would be the wavelength of the same sound in water?

  18. Example • The red light emitted by a He-Ne laser has a wavelength of 633 nm in air and travels at 3 * 10 ^8 m/s. Find the frequency of the laser light.

  19. Echo Problem • A sound wave traveling at 343 m/s is emitted by the foghorn of a tugboat. An echo is heard 2.60 s later. How far away is the reflecting object?

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