WAVES – Chpt. 14WAVES – Chpt. 14

What in the World Will I Learn?What in the World Will I Learn?

You will determine how waves transfer You will determine how waves transfer energy.energy.

You will learn the parts of a wave. You will learn the parts of a wave. You will describe wave reflection and You will describe wave reflection and

discuss its practical significance. discuss its practical significance.

The Big Bad Truth First! The Big Bad Truth First!

Scientists have a Scientists have a theorytheory about waves and about waves and particles. particles.

What ever could this be called?What ever could this be called? Why does Mrs. Warren think this is Why does Mrs. Warren think this is

important for me to know? important for me to know?

Wave – Particle DualityWave – Particle Duality

Let’s use an analogy from Leonard!

WavesWaves

WAVESWAVES

Carries energy from one place to another Carries energy from one place to another Classified byClassified by what what they move through they move through

1.1. Mechanical WavesMechanical Wavesthe energy is transferred by vibrations of medium the energy is transferred by vibrations of medium (medium = matter)(medium = matter)ex/ ocean waves move through waterex/ ocean waves move through water

2.2. Electromagnetic waves (EM Waves)Electromagnetic waves (EM Waves)the energy moves through disturbances in the the energy moves through disturbances in the electromagnetic field.electromagnetic field.

a disturbance that transfers energy

MECHANICAL WAVESMECHANICAL WAVES

travel through & gradually lose energy to that medium

Examples:Examples: water, sound, rope, & water, sound, rope, &

spring wavesspring waves

Mechanical Media:Mechanical Media: water, air, rope, springwater, air, rope, spring

require a medium (the material through which the

disturbance is moving) to transmit energy

Making a pulse

Slinkin’ into WavesSlinkin’ into Waves Working in your groups answer the following questions: Working in your groups answer the following questions: 1. What do you think the difference is between a 1. What do you think the difference is between a wave pulsewave pulse and the and the wave’s wave’s

vibrationvibration? ? Place the slinky on the floor. One person should hold one end of the slinky Place the slinky on the floor. One person should hold one end of the slinky

still, while the other person begin moving the slinky up and down. still, while the other person begin moving the slinky up and down. 2. What happens when you move the slinky up and down? What happens 2. What happens when you move the slinky up and down? What happens

when you increase your speed? Which direction is the wave pulse? Which when you increase your speed? Which direction is the wave pulse? Which direction is the vibration? direction is the vibration?

Again, place the slinky on the floor. One person should hold one end still, and Again, place the slinky on the floor. One person should hold one end still, and the other person should move the slinky in a horizontal direction (it’s like giving the other person should move the slinky in a horizontal direction (it’s like giving the slinky a push).the slinky a push).

3. Look very closely to the slinky. Do you see anything while watching the 3. Look very closely to the slinky. Do you see anything while watching the slinky? Describe what you see. Which direction is the wave pulse? Which slinky? Describe what you see. Which direction is the wave pulse? Which direction is the vibration? direction is the vibration?

4. What’s the difference between the 2 types of waves you experimented with?4. What’s the difference between the 2 types of waves you experimented with?

MECHANICAL WAVESMECHANICAL WAVESClassified by how medium vibrates

Pulse = direction of energy transfer; more specifically, a single bump or disturbance in a medium.

           

           

Vibration = direction of vibration of medium relative to pulse

3 types: Longitudinal, transverse, surface

MECHANICAL WAVESMECHANICAL WAVESClassified by how medium vibrates

Longitudinal Waves:Vibration is in the same direction as

wave pulse (parallel to wave pulse)

Transverse Waves:Vibration is at 900 (right angles) to wave pulse

Surface Waves:Vibration is circular Ex/ Ocean waves

MECHANICAL WAVESMECHANICAL WAVES

Small Video discussing the differences between types of waves.

Surface WavesSurface Waves

TRANVERSE WAVESTRANVERSE WAVESVibration is perpendicular to the direction of the motion of the wave

           

LONGITUDINAL WAVESLONGITUDINAL WAVES

Also called compression or pressure waveAlso called compression or pressure wave

Examples:Examples: P-type earthquake wavesP-type earthquake waves Sound wavesSound waves

Vibration is parallel to the direction of the motion of the wave

Rarefraction (expansion)

Compression

Connecting Physics and EarthConnecting Physics and Earth

P Wave Earthquake P Wave Earthquake Waves # 1Waves # 1

P Wave Example #2P Wave Example #2 S wave Earthquake S wave Earthquake

#1#1 S Wave Example #2S Wave Example #2

Waves describe the EarthWaves describe the Earth

S waves move through solids only!!!

P waves move through solids & liquidsP waves move through solids & liquids

Are these MECHANICAL WAVES????

YES!! Seismic waves need a medium (the earth!)

WAVE STRUCTUREWAVE STRUCTURE

CREST (peak)AMPLITUDEresting to max peak

WAVELENGTH

TROUGH

AMPLITUDEAMPLITUDE Measures Measures DISPLACEMENTDISPLACEMENT

Distance between “rest & crest” or “rest & trough”Distance between “rest & crest” or “rest & trough”

Gives indication of “power” Gives indication of “power” or “strength” of waveor “strength” of wave(magnitude of earthquake = (magnitude of earthquake = Richter scale)Richter scale)

Does not affect Does not affect

velocity of wavevelocity of wave

Determines loudness (sound) or brightness (EM wave)Determines loudness (sound) or brightness (EM wave)

WAVELENGTH WAVELENGTH Distance between any two repeating Distance between any two repeating

points on a wave (also called a points on a wave (also called a cycle)cycle)

crest-crest, crest-crest, trough-trough,trough-trough,expansion-expansion, compression-expansion-expansion, compression-compressioncompression

Determines what colorsDetermines what colorswe see; what notes we hear (pitch)we see; what notes we hear (pitch)

Shorter wavelengths have more Shorter wavelengths have more cycles per minute because they cycles per minute because they aren’t as longaren’t as long

VELOCITY VELOCITY vv the rate at which the the rate at which the

energy travelsenergy travels; ; speed & direction because speed & direction because it’s a ….it’s a ….

Depends on mediumDepends on medium Mechanical waves travel Mechanical waves travel

faster through dense faster through dense mediumsmediums

EM Waves are faster EM Waves are faster through less dense through less dense mediumsmediums

Frequency Frequency ƒƒ

measured in measured in wavelengths/second or wavelengths/second or cycles/secondcycles/second

HertzHertz (Hz) = number of (Hz) = number of wavelengths in 1 secondwavelengths in 1 second

Frequency is related to Frequency is related to velocity and wavelength:velocity and wavelength:

vv = = ƒ ƒ

How oftenHow often number of wavelengths that pass any point in 1 second.number of wavelengths that pass any point in 1 second.

PERIOD TPERIOD T

How longHow longAmount of time for one wavelength to pass a pointAmount of time for one wavelength to pass a point

Related inversely to frequencyRelated inversely to frequency

11 == 11

TT ff

PeriodPeriod == 11

FrequencyFrequency

Example Time! Example Time!

A sound wave has a frequency of 262 Hz A sound wave has a frequency of 262 Hz and a wavelength measured at 1.29 m. and a wavelength measured at 1.29 m. Part a) What is the speed of the wave?Part a) What is the speed of the wave? Part b) How long will it take the wave to travel Part b) How long will it take the wave to travel

the length of a football field, 91.4 m? the length of a football field, 91.4 m? Part c) What is the frequency of the wave?Part c) What is the frequency of the wave?

Let’s break it down ya’ll! Let’s break it down ya’ll!

Example Part aExample Part a

A) What is the speed of the water? A) What is the speed of the water?

frequency = 262 Hz, wavelength frequency = 262 Hz, wavelength = = 1.29 m 1.29 m

vv = = ƒ ƒ Which variable are we solving Which variable are we solving

for? for?

Let’s plug it in!!Let’s plug it in!!

Example Part bExample Part b

How long will it take the wave to travel the How long will it take the wave to travel the length of a football field, 91.4 m? length of a football field, 91.4 m?

Example Part cExample Part c

Find the frequency from the period. Find the frequency from the period. We knew period, we know the equation, we We knew period, we know the equation, we

need to find frequency. need to find frequency.