What are waves?

Everyday examples of waves

WaveDefinition: A vibration or disturbance that transfers energy from place to place Some waves need a medium, a medium is the material through which a wave travels

2 Types of WavesElectromagnetic Waves travel through empty space and do not require a medium. (ex. Radio, microwaves , infrared, visible light, UV, x-rays, gamma rays)Mechanical Waves are waves that require a medium. (sound, water waves, rope waves)

MediumA medium is a substance that mechanical waves travel through. A solid, liquid, gas or plasma.List at least three examples of each.What is the best medium for substances to travel through?

MediumThese media are distinguished by their properties - the material they are made of and the physical properties of that material such as the density, the temperature, the elasticity, etc. Such physical properties describe the material itself, not the wave.

Not all waves require a medium to travel.

Mechanical Waves are waves that require a medium.

Electromagnetic Waves can travel through empty space and do not require a medium. But they can travel through a medium also.

DemonstrationCell phone in Bell Jar

Ring with airRing without airLeave a message – Do you think the message got to the phone? Why or Why not?

Why does sunlight reach us here on Earth while the sound of nuclear reactions happening on the sun does not?

DemonstrationThe medium that a mechanical wave travels through affects its speed.

Tap table and listenNow tap with your ear on tableTalk to someone with your lips on a balloonHangerOven racks

What causes waves?Waves are created when a source of energy causes a medium to vibrate.A vibration is a repeated back and forth or up and down motion.

A wave transports energy not matter

• When a wave is present the individual particles of the medium are only temporarily displaced from their rest position.

• There is always a force acting upon the particles that restores them to their original position.

And in a stadium wave, each fan in the bleacher ultimately returns to its

original position.

In a slinky wave, each coil of the slinky ultimately returns to its

original position.

Harmonic MotionHarmonic Motion is motion that repeats itself, oscillating back and forth. Eventually it will lose energy and come to rest in the middle, known as its equilibrium position.

Pendulum WavesWatch AsFifteen uncoupled simple pendulums of monotonically increasing lengths dance together to produce visual traveling waves, standing waves, beating, and (seemingly) random motion.

DemonstrationDo the wave!

You were a particle of the substance through which the wave traveled. Did you change your location in the room from start of generating the wave to your final position once the wave had passed?Waves transfer energy from one location to another, but they cannot transfer matter.

Lab: Slinkys in ActionUse a slinky to make different types of waves.Notice how the ribbon moves with each different type of wave.

Where did the energy come from to start the wave?

How could you tell the wave carried energy?

Types of waves: Waves are classified according to

how they move.

Transverse Wave

Teacher’s Domain Animation

Pick a point and trace a particle as the wave travels through the medium.How does the particle move with respect to the direction of the wave?

Transverse wave (sometimes called a sine

curve or wave)

Waves that move the medium at right angles (perpendicular) to the direction in which the waves are traveling is called a transverse wave 3:15min.

Transverse means across. The highest parts are called crests the lowest parts are called troughs.

Draw & Label a Transverse Wave

Compressional or Longitudinal Wave

Matter vibrates in the same direction (parallel) as the wave travels.Longitudinal discussion 3:36 min

Compressional or Longitudinal wave

The parts, where the coils are close together are called compressions, the parts where the coils are spread out are called rarefactions.

Teacher’s Domain animation

DemonstrationNew Age Wave – Students stand up in a line, shoulder to shoulder, facing the front – As one student runs past them have each student bump the student beside them in the shoulder

You were a particle of the substance through which the wave traveled. Did you change your location in the room from start of generating the wave to your final position once the wave had passed?Waves transfer energy from one location to another, but they cannot transfer matter.

Draw & Label a

Compressional/Longitudinal Wave

Longitudinal Wave

If this wave represents the sound of my voice, how could I increase the amplitude?How does frequency change with pitch?

Animation

Animation #2

DemonstrationDucky in tank –

Make water waves by repeatedly tapping the surface of the water.Note that the waves travel through the water, from right to left, while the toy bobs up and down with some side to side motion

Combinations of wavesSurface waves are a combination of transverse and longitudinal waves. The waves occur at the surface between water and air. They travel in circles

Surface Wave Animation

Summary of Waves

When the waves reach the bottle the bottle move up and down but not forward so …the waves do not transfer matter.

What is the maximum displacement of a particle by this wave?

10 m

-10 m

Summary of Waves - NASA Launch Pad Video Clip

Surface Waves

• .

Describe the motion of the ball as the wave passes.

Does this wave consist of LONGITUDINAL, TRANSVERSE, or BOTH wave types?

Earthquakes also produce this wave type.

Let’s ThinkAfter water waves move thru a pond, have the molecules of water moved or are they in their original position?

So what moves with the water?

Earthquakes

Earthquakes

Let’s think…Think about the last time you watched a live interview on TV when the interviewer was in a different location than the interviewee. There is often a delay between the interviewer asking the question and the interviewee responding. Can you think of why there might be a delay?

Different kinds of waves travel at different speedsExamplesElectromagnetic waves = visible light travel at 300,000 km/sMechanical waves = sound wave travel at .343 km/s at room temp. through airOther examples: Lightning and thunder, bat striking ball, ear on train tracks, tin can demo

What is the medium for an earthquake?

Types of Earthquake waves

P waves – Compressional

Travel through solid, liquids, gases

S waves – Transverse, shear, surface

Travels through solid only

Demo: Movement of S and P Waves

Students illustrate bonds in a solid – Push from behind P Waves

Compressional waveWhat will happen as the energy propagates through the solid?

Reference YouTube video

Students illustrate solid bonds – Grab arm and Pull backward and forward S Waves

Also called Transverse wavesShear WavesSurface Waves

Travel easily through solids

Reference YouTube video

Students illustrate a liquid – Push from behind P - waves

Why did the wave propagate?Compressional waves will still travel through a liquid.They travel through solids, liquids, and gases.Not touching about 3

inches away

Students illustrate a liquid – Close but not touching – Grab arm and Pull back to front

S-Waves – (also called shear, transverse, surface waves)

Why didn’t the wave propagate?S waves only travel through solids.S waves need chemical bonds to transfer energy

Review, Review, Review…What does a wave carry?

How can waves be generated?

Compare and contrast a longitudinal and transverse wave.

Properties of Waves

Basic Properties of WavesAmplitudeWavelengthFrequencySpeed

AmplitudeAmplitude is the maximum (displacement) distance the particles of the medium carrying the wave move away from their rest positions.

AmplitudeThe farther the medium moves as it vibrates the larger the amplitude of the resulting waves. The greater the amplitude the greater the amount of energy

Amplitude of transverse waves

You can find the amplitude of a transverse wave by measuring the distance from rest to crest or rest to trough.

Amplitude of a longitudinal wave.

The amplitude of a longitudinal wave is a measure of how compressed or rarefied the medium becomes.

Amplitude and Energy

WavelengthA wave travels a certain distance before it starts to repeat. The distance between two corresponding parts of a wave is its wavelength.

WavelengthTransverse waves measure wavelenght from crest to crest or trough to trough.

WavelengthLongitudinal waves measure wavelength from one compression to the next.

FrequencyThe number of complete waves that pass a given point in a certain amount of time.AKA number of vibrations per second.

Frequency

Frequency measured in hertz (Hz) named after Heinrich Hertz who discovered radio waves in 1886.

Frequency Animation

PeriodThe period of a wave is the time for a particle to make one complete cycle. Frequency is the inverse of Period

Pair ShareIs there a relationship between wavelength and frequency? What is it?

Is there a relationship between frequency and period? What is it?

Is there a relationship between amplitude and frequency? What is it?

SpeedThe speed, wavelength, and frequency of a wave are related to each other by a mathematical formula.

SpeedSpeed = wavelength x frequencyFrequency = speed/wavelengthWavelength = speed/frequency

SpeedWhat can effect the speed of a wave?

Wave speed depends upon the medium through which the wave is moving. Only an alteration in the properties of the medium will cause a change in the speed.

Speed Of a Wave– What do you remember

about Earthquakes?

1. A teacher attaches a slinky to the wall and begins introducing pulses with different amplitudes. Which of the two pulses (A or B) below will travel from the hand to the

wall in the least amount of time? Justify your answer.

They reach the wall at the same time. Don't be fooled! The amplitude of a wave does not affect the speed at which the wave travels. Both Wave A and Wave B travel at the same speed. The speed of a wave is only altered by alterations in the properties of the medium through which it travels.

2. The teacher then begins introducing pulses with a different wavelength. Which of the two pulses (C or D) will travel from the hand to the wall in the least amount of time ? Justify your

answer.

They reach the wall at the same time. Don't be fooled! The wavelength of a wave does not affect the speed at which the wave travels. Both Wave C and Wave D travel at the same speed. The speed of a wave is only altered by alterations in the properties of the medium through which it travels.

3. Two waves are traveling through the same container of nitrogen gas. Wave A has a wavelength of 1.5 m. Wave B has a wavelength of 4.5 m. The speed of wave B must be ________ the speed of wave A.a. one-ninthb. one-thirdc. the same asd. three times larger than

Answer: CThe medium is the same for both of these waves ("the same container of nitrogen gas"). Thus, the speed of the wave will be the same. Alterations in a property of a wave (such as wavelength) will not affect the speed of the wave. Two different waves travel with the same speed when present in the same medium.

4. TRUE or FALSE:Doubling the frequency of a wave source doubles the speed of the waves

FALSEThe speed of a wave is unaffected by changes in the frequency.

SpeedWaves in different mediums travel at different speeds. However, in a given medium and under the same conditions the speed of the wave is constant.

Chapter 15 -3

Let’s think…Have you ever been to a concert or musical event in a hall where there was ‘bad acoustics’. What did this sound like? What do waves do that could have been causing this to happen?

Ways Waves InteractReflectionRefractionDiffractionInterference

ConstructiveDestructive

Standing Waves

ReflectionWhen an object or wave hits a surface through which it cannot pass, it bounces back.

Angle of incidenceAngle of reflection

Examples of reflectionMirrorEchoBall against a wall

Refraction is when a wave moves from one medium

into another medium at an angle, it changes speed as

it enters the second medium which causes it to

bend. The bending of waves due to a change in speed is called refraction.

RefractionThough all waves change speed when they enter a new medium. Bending occurs when one side of the wave enters the new medium before the other side

DiffractionWhen a wave passes a barrier or moves through a hole in a barrier it bends and spreads out.

Let’s thinkWho has seen the large headphones that airport workers out on the tarmac or those operating large machinery wear? Do they just cover one’s ears, or is there more to them?

Those Headphones contain…

small microphones that collect incoming sound waves. Circuitry inside the headphones process this noise and reproduce the noise in a form exactly out of phase with the original. This out-of-phase version is played back to the person wearing the headphones. Due to destructive interference, a quieter background is the result.)

InterferenceConstructive interference occurs whenever two waves combine to make a wave with a larger amplitude.

Destructive interference when the amplitudes of two waves combine producing a smaller amplitude.

Superposition Example

Standing waves:If the incoming wave and the reflected wave combine at the right places the combined wave appears to be standing still.It appears to be standing in one place, even though it is two waves interfering as they pass through each other.Brightstorm video 9:45 min

Nodes and AntinodesNodes: at certain points, destructive interference causes the two waves to combine and produce an amplitude of zero.

Antinodes are the points of maximum energy. The crests and troughs of a standing wave.

ResonanceMost objects have a natural frequency of vibration. Resonance occurs when vibrations traveling through an object match the object’s natural frequency.An object that is vibrating at its natural frequency absorbs energy from the objects that vibrate at the same frequency. Occurs in music.