# Acoustics I

## 19 terms

### 3 waves of sound

- mechanical wave

- longitudinal wave

- pressure wave

### Mechanical wave

energy of this wave is transferred by particles in a medium

### Energy Vibrating body Elastic medium Receptor (human ear)

4 requirements for the production of sound

### Elastic medium

a medium consisting of molecules that can vibrate
(ex: air, water)

### Elasticity Inertia (These two forces interact during the process of vibration)

2 properties of a vibrating body

### Inertia

tendency of an object to remain at rest if left undisturbed or to remain in motion one set in motion.

### Simple Harmonic Motion (SHM)

is the repeatable pattern of vibration, and consists of a relationship between elasticity and inertia
(In the real world, friction and gravity are forces which will cause dampening, and eventually stopping, of SHM)

### Properties that characterize a sound wave

Frequency

Amplitude: distance vibrator moves from
its resting position

Phase angle: portion of cycle that has been completed at a given instant in time relative to starting point of 0 degrees

### Frequency

number of completed cycles in 1 second, measured in Hertz (Hz), is expressed in cycles/seconds

### Period

Defined as the amount of time it takes a sine wave to move from any given point in its cycle and return to the same point (the amount of time it takes a wave to complete one cycle), is expressed in 1/Hz

### Amplitude

Refers to distance a vibrating object moves from its point of equilibrium (resting position)

is related to perception of loudness and indicates intensity (power) of signal. Intensity is measured in decibels (dB)

### Phase Angle

represents the portion of the cycle that has elapsed at any given instant in time relative to some arbitrary starting point (usually zero degrees)

### Starting Phase

term used when describing phase angle of a single sine wave

### Relative Phase

term used when describing the relative timing between two or more sine waves

### Longitudal Wave

particle movement is
in the same direction as wave movement
-Sound waves traveling through air are longitudinal waves
(Flag)

### Transversal Wave

particle movement is perpendicular to wave movement
-Sound waves can be transverse in a solid.
(Desert Snake)

### Compression

areas of high density where the molecules are close together - small but measurable increase in air pressure relative to a resting state

### Rarefaction

areas of low density where the molecules are far apart - small but measurable decrease in air pressure relative to a resting state

### Velocity

Speed in a certain direction
Applied to sound, velocity refers to the speed at which the vibrations propagate through the medium. Velocity is a constant figure in a particular medium.