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Waves. Waves. Wave: A periodic disturbance in a solid, liquid, or gas as energy is transmitted through a medium (such as air, water, or rock). Wave Structure.
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Waves • Wave: A periodic disturbance in a solid, liquid, or gas as energy is transmitted through a medium (such as air, water, or rock).
Wave Structure • The 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 Waves • Wind 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.
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)/
Rogue Waves • Caused 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 Diffraction • Wave changing direction due to an obstacle like a breakwater or jetty.
Wave Reflection • Waves 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.