Waves, Currents, and Tides (S6E.3.d) Ocean Tides: A tide is the periodic rise and fall of the water level in a large body of water. High tide is a water level higher than the average sea level. Low tide is a water level lower than the average sea level. Tides on Earth are caused mainly by the pull of the moon’s gravity. The sun’s gravity affects Earth’s tides, although not as strongly as the moon’s gravity. Tidal range is the difference in levels of ocean water at high tide and low tide. Spring tide occurs when the sun’s effect is added to the moon’s effect so that the tidal range is maximized. The sun, Earth, and the moon form a straight line causing the largest tidal range. Neap tide occurs when the sun’s effect cancel the moon’s effect so that the tidal range is reduced. The sun, Earth, and the moon are at a 90° angle causing the smallest tidal range. Most locations on Earth have two low tides and two high tides each day. Because the moon revolves around Earth slower than Earth rotates, the cycle of tides is slightly longer than 24 hours.

Waves, Currents, and Tides (S6E.3.d) Ocean Waves: Some properties of a wave are size, frequency, wave period, wave speed. Ocean waves are caused primarily by wind. Other causes are earthquakes, volcanos, landslides, and meteorites/Asteroids. A wave has a crest(highest point) and a trough(lowest point). Wavelength is the distance between waves. The height of a wave from its rest position to the crest is called the amplitude. Wave period is the number of waves produced in a given amount of time. Wave speed is how fast a wave travels. A mechanical wave requires a medium, such as air or water, through which to travel. Mechanical waves carry energy through matter. As wind passes over the ocean’s surface, friction causes the water to ripple. Water does not move with a wave; it rises and falls in circular movements. Circular motion disappears about half a wavelength below the surface. Wave energy decreases as water depth increases. When a wave moves through water, energy travels and water rises and falls but stays in the same place. Ocean waves transfer energy to the shore; water at the wave bottom slows, but water at the top travels at the original speed. Waves break as gravity pulls crests down. A tsunami is a giant ocean wave that forms when a large volume of ocean water is suddenly displaced. When a wave reaches the shore, energy decreases with depth, it transfers energy to the shore, and it breaks in shallow water.

Waves, Currents, and Tides (S6E.3.d) Ocean Currents: Ocean currents are stream like paths of water in the ocean. A surface current is an ocean current near the surface caused by wind. The Coriolis effect causes surface currents to curve right or left. Continental deflection causes currents to change directions when flowing toward land. Energy from surface winds can transfer to water, causing surface currents. A deep current is a stream like movement of ocean water far below the surface. It forms when surface water becomes denser than water below, causing it to sink and become a deep current. A convection current is any movement of matter resulting from density differences. Convection currents transfer energy when warm water is moved to colder regions. Upwelling is the movement of deep, cold, nutrient-rich water to the surface. Upwelling brings nutrients from the deep ocean to the surface. Surface and deep currents and upwelling move ocean water through ocean basins. Matter transported by currents includes water, dissolved solids and gases. Energy is transported from areas near the equator toward Earth’s poles.

Waves and Currents Video https://www.youtube.com/watch?v=3qETXLc9mr8 Tides Video https://www.youtube.com/watch?v=ZQB4S8gzyIM Spring and Neap Tide Song https://www.youtube.com/watch?v=KFYf_it461s