Lecture 2- Simple Harmonic Motion

Question 1

Define starting phase. Define instantaneous phase.

Answer 1

Starting phase

• the phase at time zero
• the phase when the first cycle begins

Instantaneous phase

• The phase at any particular moment in time
• Can be plotted as a function of time
• Changes over time

Question 2

What are measures of amplitude? How can you calculate the different measures?

Answer 2

1. Instantaneous amplitude
   - the amplitude of a variable quantity observed at any given moment of time
2. Maximum Amplitude
   - the amplitude at the peak
3. Peak-to-peak amplitude
4. Root-Mean-Square Amplitude (rms)
   - the standard deviation of all instantaneous amplitudes
   - the square root of the mean of the squared deviations of instantaneous values
5. Full-Wave Rectified Average
   - represents both the peaks and the troughs
6. Half-wave Rectified Average
   - only considers the peaks

Question 3

What are the effects of friction on vibratory motion?

Answer 3

• friction limits velocity
• If amplitude of vibration diminishes over time, vibrations are damped
• In simple harmonic motion, damping varies sinusoidally over time: it is phase with velocity
• As velocity increases, kinetic energy is transformed to thermal energy: system is damped
• Magnitude of displacement depends on force applied
• Duration of vibration depends on magnitude of damping re: force applied

Question 4

Define free and forced vibration.

Answer 4

Free Vibration
- once energy imparted to a body with low damping factor, body vibrates freely

Forced Vibration

• system forced to vibrate by sound external object
• most real-world acoustic situations are forced vibrations

Question 5

Define diffraction.

Answer 5

• The bending of sound by objects in a sound field

Reflection:
- the sound or light that rebounds off of the new medium

Refraction
- the sound or light that travels through the new medium

Question 6

Define Inverse Square Law

Answer 6

• Any physical law stating that a specified physical quantity or intensity is inversely proportional to the square of the distance from the source of that physical quantity
• For every doubling of the distance from the sound source in a free field situation, the sound intensity will diminish by 6 decibels