1 What are waves? These are just one of many examples of waves

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What are What are waves?waves?

These are just one of many examples of waves...

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Waves Are a Form of Harmonic MotionMotion that repeats over and over…

The pendulum is an example.

“There and Back Again” -- this represents 1 cycle or “period.”

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Scientists use pendulums to determine predictable cycles in things such as:

Because these cycles are predictable,we can use them to “mark” time.

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Rhythmic disturbances that carry energy

through matter and space

(Harmonic Motion)

Results when matter vibrates.

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Waves are made when you speak.

Waves can travel through space.

Waves c

an make th

e

earth m

ove and shake.

And make the light you see as light.

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Waves can

travel through a medium.

is the material in which a wave moves.is the material in which a wave moves.

How dolphins communicate

Solid – earth quake

Music from your radio to your ear

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But there are some waves that don’t travel through a medium…

Electromagnetic waves such as visible light travel throughout

“matter-less” space.

More on this later...

Radio

Microwaves

Infrared Ultraviolet

VisibleX-Ray

Gamma

Larger Waves Smaller Waves

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Waves can be easily understood through...

...a wave whose oscillations are perpendicular to the direction the wave

travels.

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Crest – top of the wave

Trough – bottom of the wave

Crest

Trough

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Am

plitu

de

Am

plitu

de

Wavelength

oror

Wavelength – distance to include 1 crest and 1 trough- represented by (ג – Lambda) symbol

Amplitude – (volume) height of crest or trough from nodal line measured in decibels (db) and is the total energy of the wave.

Nodal Line

Nodal Line-resting line

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Wave frequency is the amount of waves that move through a point

per secondand is measured in the units of Hertz (Hz).

The frequency would be 3 Hz.

Point APoint A

The diagram above shows 3 waves going through point A in 1 second.

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Calculating the Velocity of a Wave

To find the velocity or speed of a wave, use the following equation:

Velocity = Wavelength X Frequency

V = ג x fV = Velocity in m/s

Wavelength in meters (m) = (ג)

f = Frequency in hertz (Hz)

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Calculating the Velocity of a Wave

A wave moves through water. The length of the wave is 5 meters. The frequency

is 2 waves per second (2 Hz). What is the velocity of the wave?

= F =V =

2 Hz5 m

10m/s

Formula Substitute Answer

V= x f 5m x 2Hz 10 m/s

Remember the 4 step process to solving equations …

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Do problems 1, 2 & 3 in your notes.

Hint: You may have to manipulate the formula – make a triangle.

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Longitudinal WavesLongitudinal WavesAlso called compressional waves.

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Longitudinal WavesLongitudinal Waves

Compression

Rarefaction

Wavelength

Rarefaction - part where molecules are spread apart

Compression - part where molecules are pushed together

Wavelength – 1 Compression and 1 Rarefaction

nodal line

amplitude

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Reflection • the bouncing back of a wave as it strikes a hard surface.• Reverberation –

• Combination of reflected waves • Multiple Echoes like in concerts

• Example: when a water wave from the ocean hits the beach

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Diffraction• when waves spread out past the edge of a barrier or through holes in the barrier.• Example: You can hear someone talking around a corner, because the waves move beyond the wall.

This is going to be a great surprise!

Not anymore!

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Refraction• To change the direction of a wave as it passes from one medium to another.• The frequency doesn’t change, but the speed and wavelength do – they slow down.

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Absorption• A wave that can be absorbed by the

medium material and disappear.• The amplitude of the wave gets smaller

and smaller. • Examples: sponge absorbs water wave

heavy curtain absorbs sound waves and dark glass absorbs light waves

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Interference• When 2 or more waves pass through a medium at the same time.Constructive Destructive

Hit the nodal line together.

Basically music.

IN PHASE

Hit the nodal line at different times.

Basically noise.

OUT OF PHASE

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Natural Frequency and Resonance

Natural Frequency– A special frequency at which objects vibrate if

they are disturbed– All things in the universe have a natural frequency– Changing the natural frequency:

• of a string-by tightness, lengthening or weight of string

• in a system-change the factors that affect the size, inertia or forces in the system.

Resonance– Having the natural frequency of the system

exactly in tune with your force-amplitude grows, Example-swing set

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Standing waves on a string

Standing wave– A wave that is trapped in one spot

Fundamental– Natural frequency of a wave

Harmonic– Fundamental and multiples of its frequency– Node-point where the string does not move– Antinode-points of the greatest amplitude– Wavelength is the length of one complete

“S” shape of the string

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Seismic Waves

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Seismic waves are vibrations that travel through Earth, carrying energy released

during an earthquake.

• Earthquakes produce three main types of seismic waves:

• P waves• S waves

• Surface waves

P waves

P waves are longitudinal waves similar to sound waves. • P waves compress and expand the

ground like an accordion.• They are the fastest seismic waves.• They can travel through both solids and

liquids.

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S waves

S waves are transverse waves, like light and other electromagnetic radiation.• S waves cause particles in the

material they pass through to vibrate at right angles to the direction in which the waves move.

• Unlike P waves, S waves cannot travel through liquids.

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Surface WavesSurface waves are waves that develop when

seismic waves reach Earth’s surface.• Surface waves move more slowly than P

waves or S waves.• Surface waves usually produce larger

ground movements and more damage than other types of seismic waves.

• Some surface waves are transverse waves, and others have a rolling motion similar to ocean waves.

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Earth’s liquid outer core blocks S

waves and refracts P

waves. The result is a

shadow zone where no

direct seismic waves from

an earthquake

are detected.