Waves and Sound - Waves Review

A vibration or oscillation is a ________________ that creates a _____ .

disturbance; wave

Wave

Transfer of energy from a vibrating source

Periodic motion

Repeated pattern of motion

Classes of waves

* Mechanical waves
* Electromagnetic waves

Mechanical waves

* Occur in matter due to movement of particles
* Require a medium
* Ex. water, sound waves (molecules of air vibrate to transmit sound energy)

Electromagnetic (EM) waves

* Caused by vibration of charged particles; wave propagates by interchanging electric and magnetic fields
* Do not require a medium and can travel through a vacuum
* Ex. sunlight, microwaves, x-rays

Cycle

A complete back-and-forth motion or oscillation

Medium

The matter or substance in which a wave moves

Rest position

Position in which particles do not experience any motion within the medium; equilibrium position

Amplitude (A)

Greatest displacement from the rest position; represents the energy of the wave

Period (T)

The amount of time to complete one cycle; measured in seconds

Frequency (f)

Number of cycles per time interval (s); measured in Hz or inverse s

f and T have a __________________ relationship, where f = 1/T and T = 1/f

reciprocal

__________________ depends on the source producing a vibration.

Frequency

The ________ depends on the medium as particles transmit the ________ .

speed; energy

Wave _________________ represents the wave’s energy and is the max displacement from the rest position.

amplitude

Only ____________ dictates amplitude.

energy

Classes of mechanical waves

1. Transverse wave
2. Longitudinal wave
3. Torsional wave

Transverse wave

Particles vibrate perpendicular to the direction of the wave motion; they “pull” one another along to transmit energy

Examples of transverse waves

Water waves, pendulum, light waves

As particles vibrate (for transverse waves), they move ________________ as the energy passes through the medium.

up and down

Longitudinal wave

Molecules vibrate parallel to the direction of the wave motion; they collide to transmit energy.

Examples of longitudinal waves

Air molecules colliding to transmit sound energy, yo-yo, bouncing up and down

Compressions

Areas in longitudinal waves where particles are closer together

Rarefactions

Areas in longitudinal waves where particles are further apart

Torsional wave

Particles move around the axis; particles vibrate circular to the direction of the wave

Examples of torsional waves

Tornado, top spinning

Periodic wave

A vibration repeated at regular time intervals; ex. water waves, radio waves, light waves

Crest

Highest point in a wave

Trough

Lowest point in a wave

Wavelength

Shortest distance between two points in a medium that are in a phase

Three ways to measure wavelength

1. Crest to crest
2. Trough to trough
3. Sin wave

As a NON-IDEAL wave travels through a medium, amplitude ____________ as energy is lost due to friction.

decreases

The frequency of a wave is only ____________________ upon its source.

dependent

_________ and _________________ may change as result of a change in medium.

Speed; wavelength

Speed is a ________________ of a medium.

characteristic

More force = higher ________________

amplitude

Less force = _________ amplitude

lower

Two ways to measure longitudinal waves

1. Compression to compression
2. Length of rarefaction

Transmitted pulse

Pulse that passes through to another medium

Reflected pulse

Pulse that returns to the original medium

Waves travel at a uniform speed if the __________ does not change.

medium

Fixed-end reflection

Inverted (crest turns into trough)

Fixed ends have more _________ _____

inertial mass

Inversion is due to Newton’s ____ law

3rd

Free-end reflection

Not inverted

At the boundary between two media: Partial reflection

Occurs because some of the energy is transmitted into the new medium while some is reflected into the original medium.

At the boundary between two media: Refraction

The change in the v of a wave that occurs when it travels from one medium to another.

Fast medium → slow medium: Transmitted/reflected waves

Transmitted wave: not inverted

Reflected wave: inverted

Fast medium → slow medium: Transmitted wave properties

f = constant

v decreases

wavelength decreases

amplitude decreases due to loss of energy

Fast medium → slow medium: Reflected wave properties

f = constant

v = constant

wavelength = constant

amplitude decreases

Slow medium → fast medium: Reflected wave properties

f = constant

v = constant

wavelength = constant

amplitude decreases

Slow medium → fast medium: Transmitted wave properties

f = constant

v increases

wavelength increases

amplitude decreases

Principle of Superposition

The resultant wave when two waves are travelling through the same medium meet; any point is the sum of each wave’s amplitude

2 pulses of different size sent down the same side meet

constructive interference

2 pulses of the same size are sent down opposite sides meet

destructive interference

Standing wave

Special case of interference which occurs when two waves of equal frequency, wavelength and amplitude are2 travelling in opposite directions in the same medium; usually occurs when a reflected wave interferes with an incident wave; wave appears to “stand still.”

Ex. musical instruments

node

point in the wave on the resting position in DI

antinode

areas midway between the nodes (max point on wave, top of amplitude) in CI

Natural frequency

Frequency exhibited when an object is allowed to vibrate freely

Resonance

response of an object that is free to vibrate to a periodic force with the same f as the natural f of the object; when resonance occurs, energy is added to a vibrating system

Ex. rippling water, earthquake, shaking windows

Fundamental frequency

Lowest natural f with the longest wavelength that will produce resonance in a string or rope; the standing wave pattern will consist of the least # of nodes/antinodes

What harmonic is the fundamental f?

1st harmonic

Overtones

all natural frequencies higher than the fundamental f (Ex. 1st overtone, 2nd overtone)

As wavelength decreases, frequency ____________________

increases

Sound waves properties

* Transmit energy
* Diffract or bend
* Reflect off of surfaces as echoes
* Require a medium
* Exhibit constructive and destructive interference

Loudness

apparent intensity of sound; relates to the amplitude

Pitch

apparent f of the sound wave; pitch may be high such as a high note on a piano or low like a low note

Quality

Used to distinguish between sounds with the same fundamental frequency but with different overtones; the sound like a single piano key would be called “pure” while a chord from an organ would be “rich.” The quality of the organ sound is higher than the single note because the frequencies of the overtones are added together resulting in a complex wave.

Oscilloscope

a device for viewing oscillations by a display on a screen

Sonic

frequencies between 20 Hz and 20,000 Hz

Audible range

The range of frequencies in which an average human ear can detect (20 Hz to 20,000 Hz)

Sound waves resonate the ear _____

drum

Infrasonic

frequencies less than 20 Hz

Ultrasonic

frequencies more than 20,000 Hz

f of average male voice

120 Hz

f of average female voice

250 Hz

Why does a male voice have a lower frequency than a female voice?

Males have longer vocal cords

Sound intensity

measurement of the rate of sound energy flowing across unit area perpenicular to the direction of the wave

What is sound intensity measured in?

Decibels (dB) (energy/unit area)

_____ dB eight hours a day is where hearing damage begins

85

Noise cancelling headphones have __________ dB rating

30-50

Friction in a medium decreases the ___________________ but not the wavelength

amplitude

speed of sound and the temp have a ___________ relationship

linear

Speed of sound increases as temperature increases due to higher _____________ energy

kinetic (so more collisions)

When sound waves interfere (2 or more waves act on the same particle), it creates fluctuation in the _____________ and amplitude

loudness

Compression meets compression

normal sound intensity

Compression meets rarefaction

minimal sound intensity

Fluctuations in sound creates _______

beats

1 beat =

one complete cycle of loud-quiet-loud

Acoustics

Nature of sound quality

Anechoic chamber

A room designed with sound absorbing materials to reduce echoes (like recording studios)

Doppler effect

The apparent shift in the pitch/f of a MOVING source relative to the observer

Sonic boom

created when an object is travelling faster than the speed of sound

Sound barrier

Intense compression of very dense air (accumulation of wavefronts) produced when an object is flying at the speed of sound

Mach number

ratio of a moving object’s v to the v of sound in air

Echolocation

Ability of some animals to determine an object’s location, direction, speed using Doppler shifts

Sonar

Device used to locate submarines and mineral deposits in oceans etc

Radar

Used to detect location of an airplane; Doppler radar used to track weather systems

Medical imaging

Ultrasound with f > 200 kHz used in pregnancy