Waves

WavesWave: A periodic disturbance in a solid, liquid,

or gas as energy is transmitted through a medium (such as air, water, or rock).

Wave StructureThe crest is the highest point above the equilibrium

position, and the trough is the lowest point below the equilibrium position.

The wavelength () is the distance between two adjacent similar points of a wave.

Wave Formation in the Ocean

What do you think causes most waves in the ocean to form?

Answer: Wind!The longer wind blows, the more

energy is transferred to the ocean’s surface causing a wave to form.

Types of WavesWind Waves- usually less than 3 meters high. Capillary wave- ripples that turn into wind

waves.Seiche- water confined to a small space like a

bay will slosh back and forth at resonant frequency.

Tsunami- Seismic wave created by an earthquake on the ocean floor.

Tides- caused by gravitational pull on the earth by the moon and sun.

Wave Movement Energy in a wave only

moves up and down in a circular-type motion.

Energy does not travel laterally (side to side).

This is why you move up and down as a wave moves past you.

Wave

Wave Heights

Factors Affecting Wave Development

1.) Mean Speed or Wind Strength- Wind must be moving faster than the wave crests for energy to transfer from air to sea.

2.) Wind Duration- High winds that blow only a short time will not generate large waves. Low winds that blow for a long time can generate very large waves.

3.) Fetch- uninterrupted distance over which the wind blows without significant change in direction. Strong wind must blow in one direction for 3 days for

large waves to be fully developed (called a fully developed Sea)/

Wave Interference

Rogue WavesCaused by positive (in phase) interference) of

waves in open ocean.Until recently, thought to be impossible.

Breaking Waves What causes a wave to crest

or “break?” Answer: As wave

approaches the coastline, the slope is shallower.

The bottom of the wave drags along the floor slowing it down.

The top of the wave continues at it’s previous speed causing it to go faster than the bottom.

This makes the wave break.

Wave Refraction Slowing and bending of

waves in shallow water. Caused due to waves

hitting shoreline at an angle.

This is why waves break at different points as they approach the shoreline

Wave DiffractionWave changing direction due to an obstacle like

a breakwater or jetty.

Wave ReflectionWaves will reflect if they hit an object straight

on. Will cause minor constructive interference.

Undertow and Rip Currents

Undertow: Formed when water breaking onto a beach is pulled back into deeper water by gravity.

Rip Currents: Form when there is a break in a sand bar. Water is quickly funneled out to sea.

Rip Currents can flow from 1-8 feet per second. That’s faster than an Olympic swimmer!

How do you escape a rip current?

Swim parallel to the shoreline!

Longshore Currents/Drift Longshore Current: Form

when waves approach the beach at an angle.

Sand is moved by these currents forming sandbars and spits.

Often called longshore drift.

Longshore Drift