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Dampened, Driven Oscillators

• Damping (result of friction, which causes the amplitude to die down

• Driving: A periodic force applied to oscillator to propell it
• Resonance : when driving period = natural period, oscillations tend to grow in amplitude
• ex. kid on a swing being pushed

CHAPTER 2: WAVES AND SOUND

wave:

1. disturbance within a medium
2. Transfers energy with no net motion of matter
1. Exception: electromagnetic waves (aka, light) need no medium

2 types of waves

• transverse : oscillations perpendicular to motion
• longitudinal: Oscillations parallel to motion
• sound waves

Ex. Earthquakes (seismic waves)

s-waves : transverse (only through solids)

p- waves : longitudinal (through solids and liquids)

• why? in the ground, molecules are strongly bound, so the oscillations can only pass perpendicular to motion. In water, molecules are not strongly bound, so the wave motion can go either perpendicular or parallel to motion.
• Application: P-waves can travel through the earth, but s-waves can not. Therefore there must be liquid in the center of the earth.

Wavelength

• denoted by λ
• note, not measured in time

A useful equation:

want relationship for velocity

d = λ (wavelength)                        and

t = T (period)

Therefore:

• if pitch goes up, f goes up and λ  goes down because v stays constant)

Ex. Sound waves

At normal temperatures and pressures

v = 340 m/s = 760 mph (note: v is independent of f and λ)

Ex: Pitches

• C = 262 Hz

• A = 440 Hz