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Waves

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Waves

Stirred by the winds into waves and pulled up and down by tidal forces, the ocean surface is always in motion.

Waves are among the most common and easily observed ocean phenomena.

Waves are periodic and predictable if the amount of energy applies to the ocean is known.

Predictable wind, earthquakes, turbidity currents, landslides, friction, and the pull of the sun and the moon all generate waves.

The sun and the moon generate the largest waves of all: the tides.

Waves

Waves are energy transmitted through matter◦ The medium ( solid, liquid, gas) not actually travel

as the energy passes through it, but its constituent particles vibrate or oscillate in place as the energy passes through them.

Definition of a wave

Typ

es/P

arts

of W

aves

Longitudinal waves (push-pull) – sound waves, the particles that are in vibratory motion push and pull in the same direction the energy is traveling.◦ Wave form travels through the medium by

compressing and decompressing

Waves

Transverse wave (side to side ) – energy travels at right angles to the direction of particle vibration◦ Generally transmits energy only through solids because

only in a solid are particles strongly bond to one another◦ These are called body waves because they transfer

energy though a body of matter

Waves

Orbital waves – waves that transmit energy along an interface between two fluids of different densities◦ Particle movements are neither longitudinal nor

transverse◦ Example: interface between the atmosphere and the

ocean. The movement of particles along such an interface involves components of both longitudinal and transverse waves because the particles move in circular orbits.

Waves

As a wave passes to the right, the motion of a floating rubber ducky resembles that of a circle, which is known as circular orbital motion

Orbital Wave

Crest – high parts of waves

Trough – low part of waves

Wave height (H) – vertical distance between the trough and crest

Wave length (L) – horizontal distance between two corresponding points

Wave steepness- H/L

Wave Characteristics

Wave period – time (in seconds) that elapses during the passing of one full wave, or wavelength

Wave frequency- the number of wavelengths that pass a fixed point per unit of time

Amplitude- Distance from level of crest to level of trough

Wave Characteristics

More stuff to talk about: Period-

Practice!!!Wave length = 5mHeight = 1mFrequency = 14/minPeriod = ?Speed = ?Steepness = ?

Practice!!!Wave length = 5mSteepness = 1/8Frequency = 3/secHeight = ?Speed = ?

Shallow-Water Waves Depth of water is above wave base, way above. (depth

< 1/20 wave length)

Waves and Water Depth

Deep-Water Waves – Depth is deeper than wave base. (depth > ½ Wave Length)

Waves and Water Depth

Transitional Waves (Between Deep and Shallow) Depth is above wave base, but only a little. (1/2 wavelength > depth > 1/20 wave length)

Waves and Water Depth

Recall:◦

◦ Wave Base = ½ Wave Length

Think: What happens if the Wave Base is decreased? How does that effect Wave Speed?

Breaking Steepness = 1/7 = H/L

Effect of Decreasing Depth

Effect of Decreasing Depth

http://www.youtube.com/watch?feature=endscreen&v=gxSDdaHzTJM&NR=1

Any Guesses?

The Cause of Waves

WIND!!!

Capillary Waves The little guys

You’ve seen these on Lucky Peak

Gravity Waves Can be huge

You’ve seen these in videos of the ocean, probably not on a lake.

Breaking waves AKA: White Caps Also on the shore Any time the steepness is larger than what?

Wave Size

Wind Generated WavesFactors important to

increasing the amount of energy transferred to the waves are:

1. The wind speed2. The duration – the

length of time during which the wind blows in one direction

3. The fetch – the distance over which the wind blows in one direction

Wind Generated WavesThe energy of a wave is directly related to

wave heightAs sea waves gain energy, their steepness

increases When steepness reaches a critical value of 1/7,

open ocean breakers called whitecaps form

Swells from different storms run together, the waves clash, or interfere with one another

Interference

Starts as a capillary wave in open sea. Grows to a gravity wave. The storm surges The swell distances itself from the storm Carries energy (in the form of waves) across

the open sea.◦ Can cause interference across the open sea

As deep water swell moves toward shore (shoaling) it enters the surf

Energy in the wave dissipates when the wave breaks.

Life cycle of a wave

Physical Changes as waves approach shore

As deep water waves of swell move toward continental margins over shoaling water, they eventually encounter water depths that are less than one-half of their wavelength

Physical Changes as waves approach shore

S waves come into shallow water and fell bottom, their speed and wavelength decrease while their wave height and wave steepness increase, this action causes waves to break

Breaking waves are analogous to a person who leans too far forward.

BreakersSpilling breakers – is a turbulent mass of air and

water that runs down the front slope of the wave as it breaks

Plunging breaker – has a curling crest that moves over an air pocket

Surging breaker- build up and break right at the shoreline.

Breakers

Rogue Waves

Massive waves that can reach 10 stories highImpossible to predict occurrence, main cause

of rogue waves is theorized to be extraordinary constructive interference

Rouge waves: Think they are Dangerous?

Some Rare Waves

http://www.youtube.com/watch?v=l_8hOai9hGQ

Wave train A series of

waves

Is it really rare?

Some Rare Waves

Breaking Steepness = 1/7 = H/L If length decreases, and height increases, what

happens to steepness?

Refracting Waves If the shore is not straight, how does the differing

speed effect the apparent direction of the wave?

Effect of Decreasing Speed

What are mechanical waves? What do they do?

What are they? Two – or three types.

Really there are only two but when combined they make a third that’s kind cool and that’s what ocean waves are, well, not all water waves, just the ones that we are used to seeing, I mean a tsunami is a wave, and made of water, and in the ocean, but its not an ocean wave, ocean waves are something more specific, and tsunamis aren’t the third kind of wave so much… But, all waves do the same thing, and what do they do?

Typ

es/P

arts

of W

aves

Review! What are the TWO types of waves? What do they add up to? Which is an ocean wave? What are some parts of a wave? How deep does the motion of a wave go?

Who can name some?

Types of waves

Ocean Waves Atmospheric waves Internal waves – “desk

top oceans” Where do these happen?

Splash Waves Tides Tsunami Human Induced

Types of waves

Ocean Waves

Shoaling

Tsunami What causes it?

Some Rare Waves

Tsunami Storm Surge Swell Shoaling Fetch Wave train Rouge Waves Breaking Waves Interference

Refracting Waves Reflecting Diffracting Gravity Waves Capillary Waves Transitional Waves Shallow-Water Waves Deep-Water Waves

Words to know:

Types of waves Waves and Water Depth

Deep-Water Waves Shallow-Water Waves Transitional Waves

Breaking Steepness = 1/7 = H/L Refracting Waves

The Cause – Wind – fig 9.8, table 9-1, Capillary Waves

Restoring force Gravity Waves Breaking Waves Life of a Wave

Rarities Rouge Waves

Interference Wave train Tsunami

What we covered today:

Create a diagram of a Wave Train which is shoaling.

Label the following parts: Crest Trough Wave length Wave height Still water level Wave Base

Open water waves Deep water waves Transitional waves Shallow water waves Breaking waves

Task to be done:

Practice!!! Wave length = 2m Height = 1m Period = 13 sec Frequency = ? Speed = ? Steepness = ?

Practice!!! Wave length = 5m Height = 10m Period = 4 sec Frequency = ? Speed = ? Steepness = ?

Practice!!! Wave length = 5m Height = 10m Period = 4 sec Frequency = ? Speed = ? Steepness = ?