Physics 11 Mr. Jean January 5th, 2012

The plan: Dates for Test Standing Waves (reviewed) Visible spectrum Doppler Effect Shock Waves Pendulum Lab tomorrow

Possible Test Dates:

Interference is a characteristic of all waves.

Standing Waves When two sets of waves of equal amplitude and wavelength pass through each other in opposite directions, it is possible to create an interference pattern that looks like a wave that is “standing still.” It is a changing interference pattern. Demo - Rope and strobe Demo - Mechanical overhead model

Visible Spectrum:

DOPPLER EFFECT Refers to the change in frequency when there is relative motion between an observer of waves and the source of the waves Doppler Movie - URL

When a source of waves and an observer of waves are getting closer together, the observer of the waves “sees” a frequency for the waves that is higher than the emitted frequency. When a source of waves and an observer of waves are getting farther apart, the observer of the waves “sees” a frequency for the waves that is lower than the emitted frequency.

All waves exhibit the Doppler effect. A particularly interesting example is used by astronomers to determine if light emitting objects (such as stars) are getting closer to us or farther away. On average most stars are moving farther away, and their light spectra are “red shifted.”

Red Shift: Moving Away from source Actual Visual Spectrum Observed Visual Spectrum

Blue Shift: Moving towards source Actual Visual Spectrum Observed Visual Spectrum

Radar bounced off a spinning planet can exhibit a Doppler effect and lead to a determination of the spin rate of the planet. This was used to discover that Venus has a retrograde spin. Of course police use the Doppler effect to catch speeding motorists.

BOW WAVES Waves in front of moving object pile up. The familiar bow wave generated by a speedboat knifing through the water is a non-periodic wave produced by the overlapping of many periodic circular waves. It has a constant shape.

Video Demonstration: Demo 2.1 – Waves & Wake from Phys123

SHOCK WAVES Just as circular waves move out from a swimming bug, spherical waves move out from a flying object. If the object flies faster than the waves, the result is a cone-shaped shock wave. There are two booms, one from the front of the flying object and one from the back.

Video Demonstrations:

Subsonic - slower than the speed of sound Supersonic - faster than the speed of sound speed of object Mach Number = speed of sound

Pendulum Mini-Lab tomorrow