# Waves.

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Waves

Waves Definition of wave
A disturbance that transfers energy through matter or space “Disturbance”-a change from a normal state

Periodic or Harmonic Motion
Motion that repeats itself in the same amount of time One repetition of motion called a cycle Examples? What does graph look like?

Periodic or Harmonic Motion
Amount of time to complete cycle called a period (T) Frequency (f) is how many complete cycles occur in one second T = 1/f or f =1/T Amplitude is the amount of displacement from rest

Graphing harmonic motion

Graphing Harmonic Motion

Homework Complete Harmonic Motion Worksheet

Waves demonstrate harmonic motion
Wave movement through matter Particles move Particles return to original position (location)

Types of Waves Based on particle motion in wave 2 types Transverse
Longitudinal

Wave Type-Transverse Particle motion perpendicular to wave direction

Wave Type-Transverse Particle motion perpendicular to wave direction

Parts of a Transverse Wave

Examples of Transverse Waves
Shaking a string Ocean waves Ripples on a pond “Stadium” or human wave Electromagnetic (radio, light, micro ect…)

Wave Type-Longitudinal
Particle motion in direction of wave

Wave Type-Longitudinal
Particle motion in direction of wave

Parts of a Longitudinal Wave
Particle motion in direction of wave

Examples of Longitudinal Waves
Sound waves Oscillating springs

Sound waves are longitudinal waves

Represent longitudinal waves as transverse waves
Particle displacement in a longitudinal wave can be graphed as a transverse wave Particle motion from rest graphed as amplitude

Sound Waves Sound waves move vibrational energy through matter
Sound waves are longitudinal waves

Wave Properties Common Characteristics of Wave
Length Height Frequency (how often they occur) Period (how long to make 1 cycle) Speed All Characteristics of Waves Can Vary

Wave Characteristics Wavelength (λ)-the distance between repeating parts of a wave Trough to trough Peak to Peak Rarefaction to Rarefaction Compression to compression - Or any other repeating part

Wave Characteristics Wave amplitude (height)-the maximum displacement from the undisturbed position of the medium to the top of a crest or bottom of a trough

The wavelength of the wave in the diagram above is given by letter ______. The amplitude of the wave in the diagram above is given by letter _____.

Indicate the interval which represents one full wavelength.

Wave Characteristics The frequency (f) of a wave is the number of complete waves (cycles) that pass the observer in a given time. Hertz is the unit of frequency, and just means how many cycles (peaks) per second.

Wave Characteristics The period (T) of a wave is the time for a wave to make one complete cycle (peak to peak). The period is related to the frequency by the following equation f=1/T

Wave Characteristics The speed (v) of a wave is the how fast the wave is moving distance the wave travels in a certain amount of time.

Wave Characteristics The relationship between the speed, frequency, period and wavelength Example: 2 waves each second (i.e. frequency = 2 Hz) the period is equal to 1/f = ½ second the distance between the waves as 25 cm: this is the wavelength. In 0.5 s, waves move 25 cm, so we can find the speed using: speed= v = λ x f = 25 x 2 = 50 cm/sec OR speed = v = λ x 1/T = 25 x (1÷ ½) = 50 cm/sec

Homework Complete Wave Worksheet

Factors Affecting the Speed of Sound
Sound waves require matter to travel No particles to compress = no waves = no sound Speed of sound depends on matter or medium Speed does not depend of the source Factors that affect the speed of sound include: Temperature of medium Elasticity of medium Density of medium

Speed of Sound Temperature Affects
Temperature changes affect sound speed more in gases than solids or liquids Particles spaced apart in gases Temperature affects spacing of particles in gases (Charles & Boyles Gas Laws) Temperature High temperature air = higher sound speed Low temperature air = lower sound speed Heat and sound = kinetic energy

Speed of Sound Elasticity
Elasticity = The tendency of an object to return to its original shape once the forces are no longer applied. Phases of matter have great effect on elasticity of matter Greater elasticity = Greater speed of sound vsolids > vliquids > vgases

Speed of Sound Density Less effect on speed of sound than elasticity
Within a single phase of matter = greater impact Density = mass/volume Within a single phase of matter Greater density = lower speed of sound Mass of heavier particles are harder to move Greater density = Greater inertia

Speed of Sound Materials Material Speed of Sound (m/s) Iron 5890 Lead
The speed of sound varies through different materials Material Speed of Sound (m/s) Iron 5890 Lead 1960 Water 1479 Ice 3980 Air 330

Sonic Boom When an object travels faster than the speed of sound it breaks the “sound barrier” Waves all traveling at same speed, pile up on each other as plane pushes them together Result is a “sonic boom”

Properties of Sound Intensity-measure of sound’s amplitude
Related to loudness, but loudness is subjective Intensity measured in decibels (dB) Increase in 10 dB results in sound that is twice as loud Source Intensity Level (dB) Threshold of hearing (TOH) Rustling leaves 10 Whisper 20 Normal conversation 60 Busy street traffic 70 Vacuum cleaner 80 Rock concert 110 Threshold of pain 130 Military jet takeoff 140 Eardrum perforation 160

Properties of Sound Frequency and Pitch
Frequency is number of waves in a certain amount of time Frequency is measured in Hertz (Hz) Pitch is related to frequency, describes how high or low the sound is. Pitch is subjective. Pitch is the sensation of frequencies High frequency = high pitched sounds Low frequency = low pitched sounds

Human Hearing and Frequency
Humans can hear frequencies ranging from 20-20,000 Hz Ultrasound are sound waves with frequencies above the human hearing range

Properties of Sound Sound Quality is referred to Timbre
Differences in timbre allow listeners to hear not only the difference between an oboe and a flute, but also the difference between two different flutes, even if both flutes are playing notes at the same frequency and amplitude

Properties of Sound Descriptions related to timbre Warm Mellow
Resonant Dark or Bright Heavy or Light Flat Having much, little, or no vibrato Descriptions related to timbre Reedy Brassy Clear Rounded Piercing Strident Harsh

Properties of Sound Doppler Effect
The observed effect between an observer and a sound source when one is moving relative to another distance decreasing → perceived frequency (pitch) is increased distance increasing → perceived frequency (pitch) is decreased

Doppler Effect Examples
(visual) (visual and audio)

Wave Interactions What is the result of collisions between waves and other waves or objects? Waves transfer energy Collisions results in energy transfer Lose or gain energy

Wave Interactions Wave colliding with other waves cause interference
Principle of Superposition Waves add (subtract) amplitudes (energy) Two kinds of interference Constructive (add) Destructive (subtract)

Sound Wave Interactions
Interference Constructive = increase in intensity Destructive = decrease in intensity

Wave Interactions Constructive Interference
waves add to produce a new wave with larger peaks than either of the two original waves

Wave Interactions Constructive interference

Wave Interactions Destructive Interference
waves add to produce a new wave with smaller peaks than either of the two original waves

Sound Wave Interactions
Interference

Phase shifts of waves The phase shift tells an observer how out of sync two or more waves are It gives the offset of the two waves In phase = constructive interference Out of phase = destructive interference

In phase and out of phase waves
Waves are completely out of phase – destructive interference Waves are completely in phase – constructive interference

Sonic Boom Constructive interference of waves = sonic boom
Crack of a bull whip = sonic boom

Standing waves on a string

Harmonics of Standing Waves

Harmonics of standing waves

Homework Complete Sound and Standing Waves Worksheets

Sound Wave Interactions
Resonance Is the vibration of an object at its natural frequency This frequency depends on the length of the object

Sound Wave Interactions
Resonance Tuning forks and bells vibrate at their natural frequency All objects have a frequency that they resonate at When waves bounce back and forth on themselves within the object and constructively interfere, we call it resonance.

Sound Wave Interactions
Resonance Examples (Movie of Tacoma Narrows Bridge)

Wave Interactions Wave colliding with objects have following 3 outcomes Refraction Reflection Diffraction

Wave Interactions REFLECTION
Reflection is when waves bounce from a surface back toward the source. A mirror reflects the image of the observer. None of the characteristics of a wave are changed by reflection. No change-wavelength, frequency, period Change-wave direction

Wave Interactions REFLECTION Law of Reflection
Angle of Incidence = Angle of Reflection

Sound Wave Interactions
Reflection When a sound wave in air reaches the surface of another material, some of the sound is reflected off the surface and some passes into the material (transmitted)

Sound Wave Interactions
Reflection Smooth surfaces best more sound will be reflected from a smooth wall made of mud than a pile of dirt reason is that the rough or porous surface allows for many reflections, resulting in more absorption and less reflection

Sound Wave Interactions
Reflections Echoes When sound reflects off a smooth flat surface, an echo or reproduction of the sound can be heard. Echoes are more noticeable if the surface is far enough away to allow for a time-lag between when the sound is made and when it is hear. (~0.1 seconds)

Echo Problem If the speed of sound in air is 340 m/sec and you hear an echo 1 sec after you yell, how far away is the reflector? Remember that that the sound wave has to travel there and back so V=total distance/time 340m/sec= total distance/1 sec Total distance = 340 m/sec x 1 sec = 340 m Distance to reflector = total distance ÷ 2 = 170 m

Wave Interactions DIFFRACTION
Diffraction is the bending of waves when they collide with the edges of objects. All waves diffract. We can hear around a corner because of the diffraction of sound waves.

Sound Wave Interactions
Diffraction Because sound waves diffract, you can hear around corners and from behind obstacles

Wave Interactions REFRACTION
Refraction is when waves are deflected when passing from one medium to another The wave generally changes direction.

Sound Wave Interactions
Refraction is the bending of waves when they enter a medium where their speed is different.

Sound Wave Interactions
Refraction-Effect Cool air-lower speed, Warm air-higher speed Normally, only the direct sound is received. But refraction can add some additional sound, effectively amplifying the sound. Natural amplifiers can occur over cool lakes.

Homework Complete Wave Interactions Worksheet

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