WAVESTypes of Waves and Their Properties

Questions of the WeekWhat is a wave?

What kinds of waves are there?

http://brightstorm.com/science/physics/vibration-and-waves/wave-characteristics/

Waves Are Everywhere!!! Waves are disturbances that transfer energy through matter or space.

Energy is the ability to do work.

There are 2 main types of waves: 1) Waves that require a medium to travel through

Waves that need a medium are called mechanical waves. A medium is the material (matter) in which a mechanical wave travels.

A medium can be a solid, liquid, gas, or a combination. All waves that travel through a medium have a source.

2) Waves that are able to travel without a medium eg. electromagnetic (light) waves can travel

through a vacuum (empty space where there is nomatter), but can also travel through a medium

We will learn more about EM waves when we talk about light later in the Unit.

Khan Academy – Introduction to Waves

Mechanical WavesMechanical waves are created

when a source of energy causes a medium to vibrate or oscillate. Vibrations are repeated up-and-

down or back-and-forth movement of molecules or objects

Sound and water waves travel through a medium. The medium requires matter A medium can be a solid, liquid, gas,

or a combination of these.

There are 3 types of mechanical waves, based on the direction the wave moves: longitudinal, transverse, and

surface

Vibrations Video #1

Transverse Waves A transverse wave is when matter in

the medium moves at right angles (perpendicular, 90°, or up and down) to the direction the wave travels. eg. a rope, electromagnetic

radiation (light), seismic waves (earthquakes)

The crest is the highest part of the wave.

The trough is the lowest point of the wave.

Rest is where the wave would be if it wasn´t moving (in the middle of the crest and the trough).

Transverse wave video Brightstorm - Transverse Waves

Longitudinal Waves A longitudinal wave

(compression wave) is when matter in a medium moves in the same direction (parallel or back and forth) that the wave travels. eg. slinky; sound

A compression is when the medium is pushed close together (or is more dense).

A rarefaction is when the medium is pulled farther apart (or is less dense).

Longitudinal wave videoTransverse vs. Longitudinal

waveBrightstorm –

Longitudinal Waves

Types of Mechanical Waves

Surface WavesA surface wave is a

combination of the two types of waves (longitudinal and transverse). The particles move in a circular

motion.

It occurs between two mediums; for example air and water.

Water moves back and forth slightly but can not compress

BrainPop - Waves

Question of the WeekIf waves are similar to one another, how

can we tell them apart?

Properties of Waves There are many different types of waves

(eg. sound, light, etc.), but all waves have the same basic shape Waves share certain properties

What distinguishes one wave from another are: The amplitude (height) of the wave The wavelength (distance) of the wave The frequency (number of waves in a certain

time) The speed (how fast) at which a wave travels

Khan Academy – Amplitude, Frequency, and Wavelength of Waves

Which Wave Has More Energy?When you go surfing, do you try to catch:

A little wave…

… Or a BIG wave?

AmplitudeThe amplitude of a wave is the

height of the crest or the depth of the trough (they are the same). In a transverse wave, amplitude is the

distance from rest to crest (or rest to trough)… but not crest to trough!

In a longitudinal wave, amplitude is how compressed a wave is.

The larger the amplitude, the greater the energy a wave has.

The smaller the amplitude, the less energy a wave has.

Amplitude videoWave Characteristics video

Which wave has the highest amplitude?

WavelengthThe wavelength (λ) is the

distance between two corresponding parts of the wave eg. in a transverse wave, it is

measured from crest to crest, or from trough to trough

eg. in a longitudinal wave, it is measured from compression to compression or from rarefaction to rarefaction

Wavelength is measured in meters (m)

Wavelength video

Frequency The frequency (f) of a wave is the

number of times the wave passes a certain point in a given time It is measured in vibrations/sec or

Hertz (Hz)

1 Hz = 1 vibration/sec or 1 wave/sec

eg. If a string vibrates three times in 10 seconds, what is the frequency?

3 vibrations/10 seconds = 0.3 vibrations/sec = 0.3 Hz

Brightstorm - Frequency

Which wave has the highest frequency? Why?

Frequency Questions1. Use the two waves on the right

to answer the following questions: a) What are the frequencies of

these waves if they pass by in 10 seconds?

b) What are their frequencies if they pass by in 1 second?

2. What happens to the frequency of a wave if we change the wavelength? As the wavelength decreases, the

frequency increases. … and vice versa: as the

wavelength increases, the frequency decreases.

Waves Song

Important Facts About WavesLight travels about 300 000 000 m/s (300 000 km/s)!Sound travels about 340 m/s (in air).

The speed of a wave depends on the properties of the medium the wave is traveling in.

eg. Sound travels faster in solids or liquids than in a gas

As long as waves travel through the same medium, their speed is unaffected by a change in wavelength or frequency because as one increases, the other decreases

The higher the amplitude of a wave, the larger its energy

The longer the wavelength, the lower the frequency and the lower the pitch (pitch is highness or lowness of sounds)

Question of the DayHow can we calculate the speed,

frequency, or wavelength of a wave?

Brightstorm - Wave Speed

Wave Calculations When talking about Energy, we learned that velocity is how fast something is moving.

velocity = distance ÷ time (or v = d/t) units: m/s = m ÷ s

When we talk about waves: the distance is wavelength of the wave (in meters); and the time is the inverse of the wave´s frequency (in 1 ÷ s or 1/s) [another name for this is the period

(T)]

So the equation to find the speed of a wave becomes: speed = wavelength x frequency … or in other words: v = λ x f

When we rearrange the formulas to solve for λ x f: v

÷ ÷ λ x f

eg. A wave has a wavelength of 1 m. If it has a frequency of 10 Hz, how quickly is it traveling? knowns: f = 10 Hz; λ = 1 munknown: v v = λ x f v = 1 m x 10 Hz v = 10 m/s

Wave CalculationsA sound wave is traveling at 340 m/s. If the

frequency is 68 Hz, what is the wavelength?

If a microwave has a wavelength of 5 mm and travels 300,000 km/s, what is its frequency?

Wave CalculationsA sound wave is traveling at 340 m/s. If the frequency is 68 Hz, what

is the wavelength? knowns: f = 68 Hz; v = 340 m/s unknown: λ v = λ x f λ = v/f λ = 340 m/s ÷ 68 Hz λ = 5 m

If a microwave has a wavelength of 5 mm and travels 300,000 km/s, what is its frequency? knowns: λ = 5 mm, v = 300,000 km/s unknown: f

Must convert to SI units (eg. meters) λ = 0.005 m, v = 300,000,000 m/s v = λ x f f = v/ λ f = 300,000,000 m/s ÷ 0.005 m f = 60,000,000,000 /s (or Hz)

Practice Wave Calculations1. A 100 waves pass by every 20 seconds. What is the

wave’s frequency?

2. Calculate the velocity of a wave if its wavelength is 30 cm and its frequency is 150 Hz.

3. Find the wavelength of a wave if it travels at 10 m/s and has a frequency of 8000 Hz.

4. What is the frequency of a light wave that has a wavelength of 30 mm?

5. A wave travels 13 km in 6.5 seconds. What is its velocity?

Practice Wave Calculations1. A 100 waves pass by every 20 seconds. What is the

wave’s frequency?0.2 Hz

2. Calculate the velocity of a wave if its wavelength is 30 cm and its frequency is 150 Hz.45 m/s

3. Find the wavelength of a wave if it travels at 10 m/s and has a frequency of 8000 Hz.0.00125 m

4. What is the frequency of a light wave that has a wavelength of 30 mm?1 x 1011 Hz (or 100 000 000 000 Hz)

5. A wave travels 13 km in 6.5 seconds. What is its velocity?2000 m/s

Practice Wave CalculationsMac and Tosh are resting on top of the water near the

end of the pool when Mac creates a surface wave. The wave travels the length of the pool and back in 25 seconds. The pool is 25 meters long. Determine the speed of the wave.

While hiking through a canyon, Noah Formula lets out a scream. An echo (reflection of the scream off a nearby canyon wall) is heard 0.82 seconds after the scream. The speed of the sound wave in air is 342 m/s. Calculate the distance from Noah to the nearby canyon wall.

Question of the DayWhat happens to a wave when it

encounters an obstacle or another wave?

Wave Behaviour and Other PhenomenaWhen a wave travels

through a medium, it will often encounter the end of the medium or some other obstacle.

This obstacle affects the way that the wave behaves.

ReflectionReflection occurs when

a wave hits a reflective surface and the wave changes direction and bounces back.

Law of reflection - the angle of incidence = the angle of reflection.eg. Ball hits wall, look in

mirror, echo

RefractionRefraction is the

change in direction of a wave due to a change in its speed. This happens when a wave

goes from one medium to another

When a wave moves from one medium to another at an angle, it changes speed and bends.

NOT the same thing as rarefaction in a longitudinal wave

DiffractionDiffraction is the bending of

waves around the edge of a barrier.eg. sound bends around

corners

Because of change of speed, waves can bend in different patternsThe amount of bending

increases with increasing wavelength and decreases with decreasing wavelength

BrainPop – Refraction vs. Diffraction

InterferenceInterference occurs when two or

more waves meet and interact with each other

Constructive interference - when two waves combine to make a wave with a larger amplitude. Constructive Interference Video

Destructive interference -when two waves meet and make a wave with a smaller amplitude or cancel each other out. Destructive Interference Video

Standing Wave A standing wave is a wave that

appears to stand in one place (constant position) This happens when two waves

traveling in opposite direction interfere with one another

A node is a point where the amplitude of the wave is zero

An antinode is the maximum energy in the wave (the crests and troughs)

Standing Wave Video Standing Wave Video #2

Resonance Most objects have a natural

frequency of vibration.

Resonance is when vibrations traveling through an object match the object’s natural vibrations.

If vibrations of the same frequency are added, the amplitude increases

eg. a swing (if you time the pushes properly, the swing moves with a large amplitude)

eg. breaking a wine glass

Many of the sounds we hear, such as when hard objects are struck (metal, glass, wood, etc), are caused by brief resonant vibrations in that object.

http://www.brightstorm.com/science/physics/oscillatory-motion/resonance/

http://www.youtube.com/watch?v=j-zczJXSxnw