NATURE OF WAVES

• Waves (Def.) – A wave is a disturbance that transfers energy.

• Medium – Substance or region through which a wave is transmitted.

• Speed of Waves – Depends on the properties of the medium.

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What is a wave?• Mechanical Wave:

– when materials oscillate (move back in forth) to transfer energy. It needs to have an initial energy input and a medium in which to travel.

• What do waves transfer then?• Energy!

• Medium – – The substance the wave travels through, can

be gas, liquid, or solid

What causes waves?

• Vibration – are the oscillations that occur in a wave.

• Can You Make Your Slinky Vibrate? Draw a picture of what your oscillations look like:

Types of waves• Transverse waves – move side to side

– Parts:• Crest – the top part of the wave• Trough – the bottom part of the wave

• Longitudinal waves – move in and out by compressing together

– Parts• Compression – close together• Rarefaction – far apart

Basic wave properties I• All waves have 4 basic properties

– Amplitude – the height of the wave

– Wavelength – the length of one complete cycle

Basic Wave Properties II

• Frequency – how often the wave occurs over a period of time.– Cycles per second. Measured in Hertz (Hz)– Example: 8 cycles in 2 seconds = 4 Hz

• Speed – the meters the wave traveled per second– Speed = 9 meters in 3 seconds = 3 m/s– Speed = wavelength x frequency

1. A wave has a wavelength of 15 cm and has a frequency of 10 waves/second. What is the speed of the wave?

2.The speed of a wave on a rope is 50cm/s and it’s wavelength is 10cm. What is it’s frequency?

3.A wave is traveling with a velocity of 125m/s and has a frequency of 20 waves/second. What is the length of the wave?

What Is Sound?What Is Sound? Sound is vibrations Sound is vibrations

that you can hearthat you can hear Waves travel as Waves travel as

longitudinal waveslongitudinal waves Sound is due to Sound is due to

vibrations that vibrations that make the make the molecules around molecules around them compress.them compress.

•Ex: Air particles are compressed and spread out•Travel at 343 meters/second

Sound Depends On:Sound Depends On:

A vibrating A vibrating sourcesource to set up to set up the sound wavesthe sound waves

A medium to A medium to carry the wavescarry the waves

A receiver to A receiver to detectdetect them them

Sound VibrationsSound Vibrations

Back-and-forth Back-and-forth movement of movement of matter or particles matter or particles of matterof matter

Sound travels Sound travels away from the away from the vibrating object in vibrating object in all directionsall directions

Reflection vs. AbsorptionReflection vs. Absorption Just like light waves, sound waves can be Just like light waves, sound waves can be

reflected or absorbedreflected or absorbed Sound waves reflect straight from a Sound waves reflect straight from a

smooth, flat surfacesmooth, flat surface There is a clear echoThere is a clear echo

Sound waves are reflected in many Sound waves are reflected in many directions from a directions from a roughrough, uneven surface, uneven surface There is no clear echoThere is no clear echo

Can sound travel in empty space??Can sound travel in empty space??

No! Because there is no medium or No! Because there is no medium or particles.particles.

Light may travel thru space because it is a Light may travel thru space because it is a particle thatparticle that

Travels in aTravels in a

Wave and Wave and

Thus does notThus does not

Need a medium.Need a medium.

Sound waves travel at all directions until it Sound waves travel at all directions until it reaches a surface where it is absorbed or reaches a surface where it is absorbed or reflectedreflected.. This is how sound waves This is how sound waves

normally travel from one source.normally travel from one source.

Sound waves from a tuning fork.Sound waves from a tuning fork. As the fork As the fork

vibrates it vibrates it causes causes particles to particles to compress compress and rarefact and rarefact (spread out)(spread out)

Wave SpeedWave Speed

A Greater Speed means either:A Greater Speed means either: A greater FrequencyA greater Frequency

Or Or A greater wavelengthA greater wavelength

Volume: Intensity/LoudnessVolume: Intensity/Loudness Amount of sound Amount of sound

energy reaching your energy reaching your earsears

Or: Or: How High the How High the Amplitude isAmplitude is

Depends on:Depends on: How far the vibrating How far the vibrating

object is moving as it object is moving as it goes back and forthgoes back and forth

How far you are from How far you are from the source of a soundthe source of a sound

Volume Control

Different Pitch:Different Pitch:

HighHigh PitchPitch is when is when LessLess MaterialMaterial vibrates vibrates with with more energymore energy: : High FrequencyHigh Frequency

LowLow PitchPitch is when is when MOREMORE Material Material vibrates vibrates with with Less energyLess energy: : Low FrequencyLow Frequency

PitchPitchThe The Higher the Frequency the Higher the PitchHigher the Frequency the Higher the Pitch..The The Lower the Frequency the Lower the PitchLower the Frequency the Lower the Pitch.. Depends on how fast the source of the sound is Depends on how fast the source of the sound is

vibratingvibrating To change the pitch:To change the pitch:

Change the length Change the length of the material vibratingof the material vibrating Change the thickness Change the thickness of the material vibratingof the material vibrating

• Example: Boom WhackersExample: Boom Whackers

Name that TuneName that TuneC C G G A A GC C G G A A GFF E E D D CFF E E D D CGG FF EE DGG FF EE DGG FF EE DGG FF EE DCC GG AA GCC GG AA GFF EE DD CFF EE DD C

The different lengths will The different lengths will cause a different frequency / cause a different frequency / notenote or vibration when or vibration when struck ORstruck OR

A lower frequency when longer A lower frequency when longer because it makes a longer because it makes a longer wavelength.wavelength.

Name that TuneName that Tune

C, C, D, C, F, EC, C, D, C, F, EC, C, D, C, G, FC, C, D, C, G, FC, C, High C, AC, C, High C, A , , F, E, D,F, E, D, AA# ,# , A A# , # , A, F, G, FA, F, G, F

Ultra SoundUltra Sound UltrasoundUltrasound or or

ultrasonographyultrasonography is is a medical imaging a medical imaging technique that uses technique that uses high frequency high frequency sound waves and sound waves and their echoes. The their echoes. The technique is similar technique is similar to the echolocation to the echolocation used by bats, used by bats, whales and whales and dolphins, as well as dolphins, as well as SONAR used by SONAR used by submarines. In submarines. In ultrasound, the ultrasound, the following events following events happen: happen:

The ultrasound machine The ultrasound machine transmits high-transmits high-frequency (1 to 5 frequency (1 to 5 megahertz) sound megahertz) sound pulses into your body pulses into your body using a probe. using a probe.

1. The sound waves travel 1. The sound waves travel into your bodyinto your body and and hit a hit a boundaryboundary between between tissues (e.g. between tissues (e.g. between fluid and soft tissue, fluid and soft tissue, soft tissue and bone). soft tissue and bone).

Some of the sound Some of the sound 2. 2. waves getwaves get reflected back reflected back

to the probe, while some to the probe, while some travel on further until travel on further until they reach another they reach another boundary and get boundary and get reflected. reflected.

The reflected waves areThe reflected waves are3. picked up by3. picked up by the probe the probe

and relayed to the and relayed to the machinemachine..

The machine displays the distances and The machine displays the distances and intensities of the echoes on the screen, intensities of the echoes on the screen, 4. 4. forming a 2D imageforming a 2D image like the one like the one shown above.shown above.

SONARSONAR

To locate a target, a To locate a target, a submarine uses active submarine uses active and passive and passive SONARSONAR ((sosound und nnavigation avigation aand nd rranging). anging). Active Active sonarsonar emits pulses of emits pulses of sound waves that sound waves that travel through the travel through the water, reflect off the water, reflect off the target and return to target and return to the ship. By knowing the ship. By knowing the speed of sound in the speed of sound in water and the time for water and the time for the sound wave to the sound wave to travel to the target and travel to the target and back, the computers back, the computers can quickly calculate can quickly calculate distance between the distance between the submarine and the submarine and the target target

Whales, dolphins and bats use the same technique as ultrasound for locating prey (echolocation).

Doppler AffectDoppler Affect Occurs as sound Occurs as sound

is made from a is made from a moving sourcemoving source

Occurs as sound Occurs as sound travels away from travels away from you or toward you or toward you.you.

Pitch is heard Pitch is heard becausebecause

Toward: higher Toward: higher pitchpitch

Away: lower pitchAway: lower pitch

As Sound Breaks the Sound Barrier As Sound Breaks the Sound Barrier it creates a loud boom!it creates a loud boom!

Occurs when Occurs when travel faster travel faster than the than the speed of speed of sound: 343 sound: 343 m/sec.m/sec.

This is This is because air because air particles particles can’t move can’t move out of the out of the way fast way fast enough.enough.

When something travels faster than than When something travels faster than than sound> Supersonicsound> Supersonic

Because Because air air particles particles don’t don’t move out move out of the way of the way it creates it creates an an additional additional wave.wave.

Making Glasses SingMaking Glasses Sing As the resonant wave As the resonant wave

moves around the glass, it moves around the glass, it drags the water molecules drags the water molecules with it, creating a wave of with it, creating a wave of water that you can see near water that you can see near the edge of the glass. The the edge of the glass. The dragging water molecules dragging water molecules effectively increase the effectively increase the mass (both the water and mass (both the water and the glass molecules) and the glass molecules) and reduce the energy of the reduce the energy of the wave traveling through the wave traveling through the glass. When the energy is glass. When the energy is reduced, so is the reduced, so is the frequency of the wave in frequency of the wave in the glass, which is reflected the glass, which is reflected in the pitch of the sound in the pitch of the sound wave that you hear.wave that you hear.

As you add more liquid in As you add more liquid in there is more vibrating there is more vibrating material and you get a lower material and you get a lower frequency and a lower pitch.frequency and a lower pitch.

http://recipes.howstuffworks.com/question603.htm

Sound Travels at Different Speeds Sound Travels at Different Speeds Through Different MaterialsThrough Different Materials

02,0004,0006,0008,000

10,00012,00014,00016,00018,00020,000

AIR WATER GRANITE

Feet per secondFeet per second

Which Would Be the Best Which Would Be the Best Conductor?Conductor?

Solid?Solid? Liquid?Liquid? Gas?Gas?

Solid – The Solid – The Bricks!Bricks!

What happens to the speed of What happens to the speed of sound if the temperature changes?sound if the temperature changes?

For the answer visit the following website: For the answer visit the following website: http://www.sengpielaudio.com/calculator-speedsound.htmhttp://www.sengpielaudio.com/calculator-speedsound.htm

Why does this happen?Why does this happen? Molecules move faster as the temperature Molecules move faster as the temperature

increase and slower as the temperature decreasesincrease and slower as the temperature decreases Because Air is the medium at which sound travels Because Air is the medium at which sound travels

it affects the speed.it affects the speed. If the temperature is the same, then the speed of If the temperature is the same, then the speed of

sound is the same on a mountian top or at ocean sound is the same on a mountian top or at ocean level level • Air Pressure and Air Density DO NOT affect speed of Air Pressure and Air Density DO NOT affect speed of

sound.sound.• Density of Materials (solids, liquids, gases) does matter!Density of Materials (solids, liquids, gases) does matter!

SAMPLE LESSON: Light & the Electromagnetic Spectrum

By D. L. Power

Revised 1/20/01

© 2000 Microsoft Clip Gallery

LIGHT: What Is It?

• Light Energy– Atoms

• As atoms absorb energy, electrons jump out to a higher energy level.

• Electrons release light when falling down to the lower energy level.

– Photons - bundles/packets of energy released when the electrons fall.

• Light: Stream of Photons• This photon travels in a wave.

© 2000 Microsoft Clip Gallery

© 2000 Microsoft Clip Gallery

Electromagnetic Waves

• Speed in Vacuum– 300,000 km/sec

– 186,000 mi/sec

• Speed in Other Materials– Slower in Air, Water, Glass

© 2000 Microsoft Clip Gallery

Electromagnetic Spectrum

© 2000 Microsoft Clip Gallery

Electromagnetic Spectrum

• Visible Spectrum – Light we can see– Roy G. Biv – Acronym for Red, Orange,

Yellow, Green, Blue, Indigo, & Violet.

– Largest to Smallest Wavelength.

LIGHT: Refraction of Light

• Refraction – Bending of light due to a change in wave speed. – Index of Refraction – Amount by which a material

refracts light.– Prisms – Glass that bends light. Different

frequencies are bent different amounts & light is broken out into different colors.

It is (mainly) reflected or refracted ?away from or towards

the normal the normal

What happens to the ray of light?

But different colours are refracted by different angles.

In fact, the ray is :• (bent through an angle), and

deviated

• dispersed (split up into separate colours)

like this.

What happens now?

R

VscreenRed is deviated most /

least ?Violet is deviated most / least ?

least

most

R

Vscreen

There is a spectrum

on the screen:

Red Orange Yellow Green Blue Indigo Violet

ROY G BIV

Resources:

• http://www.kettering.edu/~drussell/demos.html