Ch. 2 Properties of Sound

What is Sound?

Vibrations; Synchronized movement of molecules

Solids as a medium for sound

Kinetic energy low relative to attractive forces; Retain shape when perturbed

Fluids as a medium for sound

Kinetic energy high relative to attractive force; shape may change when perturbed.

What is pressure?

The force generated by molecules running into walls
of an enclosure, or into each other

Ambient Pressure

the amount of force per area of surface

Speed of sound in air

343 m/s

What increases Ambient pressure

faster movement which leads to increased kinetic energy and more molecules which leads to more collisions

How are Sound waves created?

Rapid movement of a structure within a medium can
compress the media, changing pressure

Condensation

compression; higher-than-average density area

Rarefaction

spreading; lower-than-average density area

Particle Velocity

Particles are experiencing translational movements as a
cohesive unit, this is the back-and-forth speed of individual molecules in the medium (like air) as they oscillate around their resting positions, transmitting the sound energy

Acceleration

Particles are experiencing translational movements as a
cohesive unit, this creates the pressure variations that are the sound

Far from moving object, molecular movements approach ambient levels, and sound is distinguished only as a __________

uniform, radiating disturbance

Near Field

area where molecular movements are significantly greater than ambient levels

Far field

area where molecular movements are no more than normal. Sound only defined as when & in what direction molecules move

______ can only be be detected in the near field

particle velocity

______ can be detected in both the near field and far fields

sound pressure

Condensation is transferred away from source
through

successive molecular collisions. No single molecule moves very far.

Propagate

the process of sound waves traveling through a medium (like air, water, or solids) by transferring energy as vibrations, creating alternating compressions and rarefactions, moving energy from particle to particle without the particles themselves traveling long distances

A single disturbance would create an _______

impulse sound

Repeated movements are ______

periodic sound

Waveform

Pressure plotted against time

Longitudinal waves on a Waveform graph

when molecular movements parallel direction of disturbance; compression forces

Transverse waves a Waveform graph

molecular movements perpendicular to direction of disturbance; only seen in solids and dense fluids due to shear force

P waves

longitudinal (compressional) wave that can through solids, liquids and gasses

S waves

transverse (Sheering) waves that can travel through solids, some liquids, but not gasses

Cycle as a property of sound

one complete oscillation of pressure above and
below ambient pressure

Period as a property of sound

is time required for 1 cycle of a wave to pass

Frequency as a property of sound

is number of cycles passing per second, and therefore is measured in “cycles/second” (Hz)

Period (s) =

1/Frequency (Hz)

Frequency (Hz) =

1/period (s)

Wavelength as a property of sound

(λ) is length (m) of one cycle

Wavelength (λ) =

Speed of sound (m/s)

Frequency (Hz)

Phase as a property of sound

is relative location of peaks in a cycle