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Plan for Today (AP Physics I)

This lecture covers the fundamentals of waves in AP Physics I, including wave motion and energy transfer through different mediums such as air and water. It distinguishes between mechanical and electromagnetic waves, explaining their properties and behaviors. Types of waves—longitudinal and transverse—are introduced with examples like slinkies and sound waves. The session also explores the speed of sound in various mediums and relevant formulas, providing practical problems to reinforce understanding. Visual aids, including illustrations of water waves, complement the concepts discussed.

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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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