Accoustics [PC120]

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The Metric System

• decimal, base -10 system
• Prefixes
• kilo = 1,000                (k)
• centi = 1/100                (c)
• mili = 1/1,000                (m)
• micro = 1/1,000,000)        (μ) greek letter mu

Ex. 1,000 m = 1 km

conversions:

X = 0.52 m

Simple Harmonic Motion

• Describes waves
• Describes many other phenomena

1. Periodic
1. phenomenon repeats itself
2. period = amount of time to repeat (T)
3. ex. rotation of the earth T = 1 day

1. Motion has a stable equilibrium
1. equilibrium point = position of natural rest
2. stable = if displaced from equilibrium, it will return to equilibrium point

1. Stability of equilibrium is caused by a linear restoring force
1. restoring force = force that pushes towards equilibrium point
2. linear = force is proportional to distance displaced
3. ex. 10 N of force is applied to a spring to displace it 4 meters.

20 N of foce is needed to displace it 8 meters. ETC.

Describing Simple Harmonic Motion

period : time it takes to complete one oscillation                (T)

Amplitude : max distance displaced from equilibrium         (A)

Frequency = # of cycles per second                         (f)

and

example : T = 0.25

Therefore f = 5 Hz

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Trigonometry

phase : an angle that tells us how much a wave has shifted

θ = degree of phase difference

• in phase: θ = 0 degrees
• out of phase: θ = 180 degrees