WAVES

Explain how forces cause waves.Explain how forces cause waves. Explain how waves transfer energy.Explain how waves transfer energy. Classify wave types.Classify wave types. Compare and contrast different wave Compare and contrast different wave

types in an experiment.types in an experiment.

You experience waves everyday. Every You experience waves everyday. Every sound you hear is a sound wave, every sound you hear is a sound wave, every sight you see depends on light waves!sight you see depends on light waves!

A A WaveWave is a disturbance that transfers is a disturbance that transfers energy from one place to another.energy from one place to another.

Waves can transfer energy over distance Waves can transfer energy over distance without moving matter the entire distance.without moving matter the entire distance.

For example: An ocean wave can travel For example: An ocean wave can travel many kilometers without the water itself many kilometers without the water itself moving many kilometers.moving many kilometers.

Water moves up and downWater moves up and down

Forces can start a disturbance, sending Forces can start a disturbance, sending a wave through a material.a wave through a material.

Rope WaveRope Wave

Water WaveWater Wave

A rope tied to a doorknob, water, and the A rope tied to a doorknob, water, and the ground all have something in common.ground all have something in common.

They are all materials through which They are all materials through which waves move.waves move.

A medium is any substance that a wave A medium is any substance that a wave moves through. Like water or a ropemoves through. Like water or a rope

Waves that transfer energy through matter Waves that transfer energy through matter are known as are known as mechanical wavesmechanical waves..

All the waves you’ve learned about so far All the waves you’ve learned about so far are mechanical waves.are mechanical waves.

An Earthquake wave is a good example of An Earthquake wave is a good example of energy transfer.energy transfer.

Waves can be classified by how they Waves can be classified by how they move!move!

Some waves transfer an up-and-down or a Some waves transfer an up-and-down or a side-to-side motion.side-to-side motion.

Transverse Wave

direction of disturbance

direction of wave

transfer of energy

http://www.cbu.edu/~jvarrian/applets/waves1/lontra_g.htm

Longitudinal Wave

direction of disturbance

direction of wave

transfer of energy

EarthquakesEarthquakes Earthquakes are capable of producing both Earthquakes are capable of producing both

transverse and longitudinal waves which travel transverse and longitudinal waves which travel through the solid structures of the Earth. When through the solid structures of the Earth. When seismologists began to study earthquake waves seismologists began to study earthquake waves they noticed that only longitudinal waves were they noticed that only longitudinal waves were capable of traveling through the core of the capable of traveling through the core of the Earth. For this reason, geologists believe that Earth. For this reason, geologists believe that the Earth's core consists of a liquid - most likely the Earth's core consists of a liquid - most likely molten. The speed of a wave is determined by molten. The speed of a wave is determined by the medium carrying the wave. the medium carrying the wave.

Learn how to measure amplitude, Learn how to measure amplitude, wavelength, and frequency.wavelength, and frequency.

Calculate a waves speedCalculate a waves speed Collect data to investigate how to change Collect data to investigate how to change

frequency in an experiment.frequency in an experiment.

HeightHeight SpeedSpeed LengthsLengths Also known as:Also known as:

AmplitudeAmplitudeWavelengthWavelengthFrequencyFrequency

A A crestcrest is the highest point, or peak, of a is the highest point, or peak, of a wave.wave.

A A troughtrough is the lowest point, or valley, of a is the lowest point, or valley, of a wavewave

E:\Animations\wslm05_pg18_graph.htmlE:\Animations\wslm05_pg18_graph.html

water level at rest

fixed point

crest

trough

AmplitudeAmplitude for a for a transverse wave is transverse wave is the distance between the distance between a line through the a line through the middle of a wave and middle of a wave and a crest or trough.a crest or trough.

Amplitude is an Amplitude is an important important measurement measurement because it indicates because it indicates how much energy a how much energy a wave is carrying.wave is carrying.

The distance from The distance from one wave crest to the one wave crest to the next crest is called next crest is called the the wavelength.wavelength.

Can also be Can also be measured from trough measured from trough to trough.to trough.

WavelengthsWavelengths

The number of waves The number of waves passing a fixed point passing a fixed point in a certain amount of in a certain amount of time is called the time is called the frequencyfrequency..

It measures how often It measures how often a wave occurs.a wave occurs.

Frequency AnimationFrequency Animation

When frequency increases more wave When frequency increases more wave crests pass a fixed point each second. crests pass a fixed point each second. That means the wavelength shortens. That means the wavelength shortens.

So, as frequency increases, wavelength So, as frequency increases, wavelength decreases.decreases.

The opposite is also true.The opposite is also true. Look at picture on page 498Look at picture on page 498

The graph of a The graph of a transverse wave transverse wave looks like a wave looks like a wave itselfitself

The graph of a The graph of a longitudinal wave longitudinal wave looks like a spring of looks like a spring of coils.coils.

Page 499Page 499

The speed of any wave can be determined The speed of any wave can be determined when both the frequency and the when both the frequency and the wavelength are known, using this formula:wavelength are known, using this formula:

Speed= wavelength * frequencySpeed= wavelength * frequency S= S= λλ f f

Look at the example on page 501Look at the example on page 501

Different types of Different types of waves can travel at waves can travel at very different speeds.very different speeds.

Light waves travel Light waves travel through air almost a through air almost a million times faster million times faster than sound.than sound.

Example: Thunder Example: Thunder and Lighteningand Lightening

In a stormy sea, 2 waves pass a fixed In a stormy sea, 2 waves pass a fixed point every second, and the waves are 10 point every second, and the waves are 10 m apart. What is the speed of the waves?m apart. What is the speed of the waves?

S= S= λλ f f S= 10 m/wave * 2 wave/sS= 10 m/wave * 2 wave/s

= 20m/s= 20m/s

1.1. What two measurements of a wave do What two measurements of a wave do you need to calculate its speed?you need to calculate its speed?

2.2. What is the top of a wave called? What is the top of a wave called? Bottom?Bottom?

3.3. What does the “Frequency” of a wave What does the “Frequency” of a wave mean ?mean ?

Describe how waves change as they Describe how waves change as they encounter a barrier.encounter a barrier.

Explain what happens when waves enter a Explain what happens when waves enter a new medium.new medium.

Identify ways in which waves interact with Identify ways in which waves interact with one another.one another.

When waves interact with materials, they When waves interact with materials, they behave predictably.behave predictably.

Scientist call these behaviors: Reflection, Scientist call these behaviors: Reflection, Refraction, and Diffraction.Refraction, and Diffraction.

The bouncing back of a wave after it The bouncing back of a wave after it strikes a barrier is called strikes a barrier is called reflection.reflection.

Water, soundWater, sound& light waves& light wavesall reflect.all reflect.

Sometimes, a wave does not bounce back Sometimes, a wave does not bounce back when it encounters a new medium.when it encounters a new medium.

RefractionRefraction is the bending of a wave as it is the bending of a wave as it enters a new medium at an angle other enters a new medium at an angle other than 90 degrees.than 90 degrees.

You have seen how waves reflect off a You have seen how waves reflect off a barrier. For example, water waves bounce barrier. For example, water waves bounce off the side of a pool. But what if the side off the side of a pool. But what if the side of the pool had an opening in it? of the pool had an opening in it?

DiffractionDiffraction is the spreading out of waves is the spreading out of waves through an opening or around the edge of through an opening or around the edge of an obstacle.an obstacle.

Occurs in all types of waves.Occurs in all types of waves.

Sound waves diffract as they pass through Sound waves diffract as they pass through an open doorway. an open doorway.

Turn on a TV and then walk into another Turn on a TV and then walk into another room. You can still hear it because the room. You can still hear it because the waves spread out.waves spread out.

InterferenceInterference is the meeting and combining of is the meeting and combining of waves.waves.

The adding of two waves is called constructive The adding of two waves is called constructive interference. It builds up, or constructs, a larger interference. It builds up, or constructs, a larger wave out of two smaller ones. Page 507wave out of two smaller ones. Page 507

Destructive Interference is when one wave Destructive Interference is when one wave attaches briefly to the trough of another wave. attaches briefly to the trough of another wave. The energy of one wave is subtracted from the The energy of one wave is subtracted from the energy of the other. Page 508energy of the other. Page 508

Explain what happens when waves Explain what happens when waves encounter a medium that they cannot encounter a medium that they cannot travel through?travel through?

Describe a situation in which waves would Describe a situation in which waves would diffract.diffract.

Describe two ways that waves are affected Describe two ways that waves are affected by interference.by interference.