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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) - PowerPoint PPT Presentation
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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)• Part of the floor/air stayed in place
Types of Waves
• Mechanical– Require a medium– Types of mechanical waves:
• E-M (electromagnetic)– Doesn’t require– Types of electromagnetic waves:
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)
Wave information
• Laser disks 11-15
Pictures of Waves
• Picture of Height of water striking a dock
Pictures of Waves• Picture of Height of water striking a dock
• T = period (time to repeat)• Lambda = wavelength (distance)• A = amplitude
Picture of Wave Continued
• Looking out over a lake with waves on it
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?
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
• Velocity of a wave is a function of the medium
Why is there the velocity difference
• Spacing of the molecules
• Air– Motion has to travel all the way over
• Water
• Steel
• How fast does an air molecule vibrate?• Around 350 m/s
Formula
• v = x/t• But since wavelength () is a distance and T is a
time. . .
• v = / T• v = * f
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?
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.
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?