The Nature of The Nature of WavesWaves

Wave:Wave:Any disturbance that Any disturbance that transmits energy transmits energy through matter or through matter or empty space.empty space.

Question:Question:Imagine your family has just returned Imagine your family has just returned home from a day at the beach. You had home from a day at the beach. You had fun playing in the ocean under a hot sun. fun playing in the ocean under a hot sun. You put some pizza in the microwave You put some pizza in the microwave for dinner, and you turn on the radio. for dinner, and you turn on the radio. Just then, the phone rings. It’s your Just then, the phone rings. It’s your friend calling to ask about homework.friend calling to ask about homework.

In the above scenario, how many In the above scenario, how many different waves were present?different waves were present?

Answer:Answer:Believe it or not, there were at least Believe it or not, there were at least five!!!five!!!

– Water waves in the oceanWater waves in the ocean

– Light waves from the sunLight waves from the sun

– Microwaves inside in the microwave Microwaves inside in the microwave ovenoven

– Radio waves transmitted to the radioRadio waves transmitted to the radio

– Sound waves from the radio, Sound waves from the radio, telephone, and voicestelephone, and voices

Medium:Medium:

A substance through A substance through which a wave can which a wave can travel (can be a solid, travel (can be a solid, liquid, or gas)liquid, or gas)

Types of WavesTypes of Waves

The two main types of The two main types of waves are:waves are:

TransverseTransverse

LongitudinalLongitudinal

Transverse WavesTransverse WavesParticles in this kind of Particles in this kind of wave move across, or wave move across, or perpendicular to, the perpendicular to, the direction the wave is going.direction the wave is going.

““moving across” and at moving across” and at “right angles”“right angles”

Example:Example:

Shaking a rope Shaking a rope “up and down” “up and down” creates a creates a transverse wavetransverse wave

The highest point The highest point of a transverse of a transverse

wave is called the wave is called the “crest.”“crest.”

The lowest point The lowest point between each between each

crest is called a crest is called a “trough.”“trough.”

Transverse WavesTransverse Waves

Trough

Crest

Longitudinal WavesLongitudinal Waves

The particles of the The particles of the medium vibrate medium vibrate back and forth back and forth along the path that along the path that the wave movesthe wave moves

Examples:Examples:Pushing a spring Pushing a spring “back and forth” “back and forth” creates a creates a longitudinal wavelongitudinal waveSound waves Sound waves

The parts of a The parts of a longitudinal wave longitudinal wave

where the particles where the particles are crowded is are crowded is

called a called a “compression.”“compression.”

A part where the A part where the particles are particles are

spread apart is spread apart is called a called a

“rarefaction.”“rarefaction.”

Longitudinal WaveLongitudinal Wave

compression rarefaction

Combinations of WavesCombinations of Waves

A combination of A combination of transverse and transverse and longitudinal waves is longitudinal waves is called a called a “surface “surface wave”wave”

Properties of Properties of WavesWaves

Properties of waves, Properties of waves, such as the height of such as the height of

waves and the distance waves and the distance between crests, are between crests, are useful for comparing useful for comparing

and describing wavesand describing waves

AmplitudeAmplitudeThe maximum The maximum distance that the distance that the particles of a wave’s particles of a wave’s medium vibrate from medium vibrate from their rest positiontheir rest position

Question:Question:What wave carries What wave carries more energy – a wave more energy – a wave with a large amplitude with a large amplitude or a wave with a small or a wave with a small amplitude?amplitude?

Answer:Answer:

A wave with a large A wave with a large amplitude carries more amplitude carries more energy because it takes energy because it takes more energy to move the more energy to move the rope farther from its resting rope farther from its resting point.point.

WavelengthWavelength

Distance between any two Distance between any two crests next to each other in crests next to each other in a wave (usually measured in a wave (usually measured in nanometers)nanometers)

1,000,000,000 nm = 1 m1,000,000,000 nm = 1 m

Wavelength:Wavelength:

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Amplitude

Rest Position Amplitude

Wavelength

Frequency:Frequency:Number of waves produced in a Number of waves produced in a given amount of timegiven amount of time

Frequency is expressed in Hertz Frequency is expressed in Hertz (Hz)(Hz)

Example: how many times a Example: how many times a bobber in a lake bobs up and bobber in a lake bobs up and downdown

F. Y. I.F. Y. I.

Hertz is the Metric Hertz is the Metric System derived unit of System derived unit of frequency and is equal frequency and is equal to one wave per to one wave per second.second.

(1Hz = 1/s)(1Hz = 1/s)

If two waves go by in If two waves go by in 10 seconds, then the 10 seconds, then the frequency is 2/10 s frequency is 2/10 s which = .2 Hz.which = .2 Hz.

Wave speed:Wave speed:

The speed at which a The speed at which a wave travels through a wave travels through a mediummedium

Wave Equation:Wave Equation:

Wavelength (λ) Greek letter lambdaWavelength (λ) Greek letter lambda

Frequency (f)Frequency (f)

Wave speed (v)Wave speed (v)

Wavelength X frequency = wave Wavelength X frequency = wave speedspeedλ X f = vλ X f = v

F. Y. I.F. Y. I.When a wavelength When a wavelength decreases (crests get closer decreases (crests get closer together), the frequency (the together), the frequency (the number of waves produced in number of waves produced in a given amount of time) a given amount of time) increases. increases.

The opposite is true as well!!The opposite is true as well!!

Wave InteractionsWave Interactions

Question:Question:

Why do planets shine Why do planets shine so brightly?so brightly?

Answer:Answer:

The planets and the The planets and the moon shine because moon shine because light from the sun light from the sun reflects off them.reflects off them.

ReflectionReflection

Reflection happens Reflection happens when a wave bounces when a wave bounces back after hitting a back after hitting a barrier.barrier.

All waves can be reflected.All waves can be reflected.

Water – You’ve seen it!Water – You’ve seen it!

Sound – echoSound – echo

Light – light waves from the Light – light waves from the sun are reflected when they sun are reflected when they strike the moon’s surfacestrike the moon’s surface

RefractionRefractionThe bending of a wave as the The bending of a wave as the wave passes from one medium wave passes from one medium to another at an angle because to another at an angle because the wave speed changesthe wave speed changes

Example: Look at a pencil in a Example: Look at a pencil in a half-filled glass of water.half-filled glass of water.

DiffractionDiffractionA change in the direction of a A change in the direction of a wave when the wave finds an wave when the wave finds an obstacle or an edge such as an obstacle or an edge such as an opening opening

Example: hearing music (sound Example: hearing music (sound waves) around a cornerwaves) around a corner

InterferenceInterferenceThe combination of two or more waves The combination of two or more waves that result in a single wavethat result in a single wave

Constructive InterferenceConstructive Interference – when the – when the crests of one wave overlap the crests of crests of one wave overlap the crests of another waveanother wave

Destructive InterferenceDestructive Interference – when the – when the crests of one wave and troughs of another crests of one wave and troughs of another wave overlapwave overlap

Standing WaveStanding WaveCertain parts of the wave are Certain parts of the wave are always at the rest position always at the rest position because of total destructive because of total destructive interference.interference.

The frequencies at which standing The frequencies at which standing waves are made are called waves are made are called resonant frequencies.resonant frequencies.

ResonanceResonance

Two objects naturally Two objects naturally vibrate at the same vibrate at the same frequency. Sound frequency. Sound produced by one object produced by one object causes the other object to causes the other object to vibrate.vibrate.