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

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?