Physics Unit '4' Waves and Sound

Terms and Definitions

Vibration

The cyclical motion of an object about an equilibrium point

Mechanical Wave

The transfer of energy through a material due to vibration

Medium

A substance or material through which a wave can travel

Transverse Waves

A wave in which the particles vibrate perpendicular to the direction of the flow of energy

Crest (Transverse Waves)

The maximum point of a transverse wave

Trough (Transverse Waves)

The minimum point of a transverse wave

Longitudinal Waves

A wave in which the particles vibrate parallel to the direction of the flow of energy

Compressions (Longitudinal Waves)

Region in a L.W in which the medium’s particles are closer together

Rarefractions (Longitudinal Waves)

Region in a L.W in which the medium’s particles are farther apart

Simple Harmonic Motion

A motion that repeats itself at regular intervals

Wavelength

The distance between two successive identical points on a wave

Phase

The x-coordinate pf a unique point of the wave

Phase-Shift

A shift of an entire wave along the x-axis

In-Phase

The state of 2 identical waves that have the same phase shifts

Out of Phase

The state of 2 identical waves that have different phase shifts

Frequency

The amount of cycles completed within a certain period of time (Unit is Hz = 1/s or s^-1)

Period

The time for a vibrating particle to complete 1 cycle

Audible Sound Waves

What humans can hear - 20 Hz / 20 000 Hz

Infrasonic Waves

Below what humans can hear - A frequency below 20 Hz

Ultrasonic Waves

Sound waves with a frequency above what humans can hear (Above 20 000 Hz)

Mach Number

The ratio of airspeed to the local speed of sound

• Mach 2 means the aircraft is moving 2 times quicker than thew speed of sound

Subsonic

When an object is moving slower then the speed of sound

• # < M1

Supersonic

When an object is moving at Mach speed between Mach 1 and Mach 5

• M1 < # < M5

Hypersonic

When an object is moving at a speed greater than Mach 5

• # > M5

Sound Barrier

When an object moves at the speed of sound, the sound waves emitted build up, producing very dense air, or intense compressions called the sound barrier

Sonic Boom

When an aircraft (or object) breaks the sound barrier

Sound Intensity

The amount of sound energy being transferred per unit area

• Unit = W/m²

Loudness

How humans perceive sound energy

Decible

The unit that refers to sound level (sound level = measure of sound intensity)

Interference

The process of generating a new wave when 2 or more waves meet

Constructive Interference

The process of forming a wave with a larger amplitude when 2 or more waves combine

Destructive Interference

The process of forming a new wave with a smaller amplitude when 2 or more waves meet

Principle of Superposition

The amplitude of 2 interfering waves is the sum of the amplitudes of the individual waves

• Wave 1 = 5 amp / Wave 2 = -3 amp

• 5 + (-3) = 2

• New Wave = Amp of 2

Free-End Reflection

A reflection that occurs where the second medium is less dense than the first medium → Reflection will have an amplitude with the same orientation as the original wave

Fixed-End Reflection

A reflection that occurs where one end of the medium is unable to vibrate → Reflection will be inverted

Standing Waves

When incoming and reflected waves interfere with each other ; the effect is a wave that appears to be still

Fundamental Frequency (1st Harmonic)

The lowest Frequency that can produce a standing wave in a given medium

Harmonics

Whole number multiples of the Fundamental Frequency

Overtone

A sound resulting from a string that vibrates with more than one frequency (The 2nd Harmonic)

Beat

A periodic change in sound intensity caused by the interference between two nearly identical sound waves

Beat Frequency

The frequency of beats produced by the interference of two waves with slightly different frequencies

• Equal to the difference in frequencies of the interfering waves

Doppler Effect

When a source of sound approaches an observer. the observed frequency of the sound increases → when the source moves away from an observer, the observed frequency of the sound decreases