Tides, Currents, and Waves

What are tides?

• Tides are changes in ocean water level that takes place in a regular pattern.

• The first scientist to explain tides scientifically was Isaac Newton

Kepler realized that the tides were affected by the moons

gravity on the water • Bernoulli - founded the equilibrium theory.

It is written that the sides of the earth facing the moon and on the opposite side of the moon, have the highest water elevation.

• Galileo compared a vessel with water in it to real water in an ocean. He did not think that the moon had anything to do with tides.

Causes of Tides

• Tides are caused by the pull of gravity between the Moon and Earth and the Sun and Earth. The Sun’s gravity has less effect because it is so far away.

• The pull of gravity pulls water away from the surface of Earth.

• How long will these people have to sit in the boat until the next high tide?

High Tides and Low Tides

• As Earth rotates water is pulled up onto the shore at parts of Earth that face directly toward or away from the Moon, causing high tides. The highest tide occurs at the Bay of Fundy on the Atlantic coast of North America

• At the same time, ocean water is pulled away from the shorelines of points on Earth that are not pulled by the Moon at that moment. These areas experience low tides.

Tide Cycle

• Cycle

Spring Tide

• The Moon takes a month to move around the Earth Twice during the month, the moon, sun and Earth line up - this occurs during the new and full moon. The gravity of the Sun and Moon combine to pull the water on Earth in the same direction. The result is an extra-high tidal bulge and an extra low tidal dip, called a spring tide.

Neap tidesDuring the moon's quarter phases the sun and

moon work at right angles, causing the bulges to cancel each other. The result is a smaller difference between high and low tides and is known as a neap tide. Neap tides are weak tides. They occur when the gravitational forces of the Moon and the Sun are perpendicular to one another (with respect to the Earth). Neap tides occur during quarter moons.

• Red tide - An event where fresh water algae accumulates rapidly

• Diurnal tides - have a single high tide and a single low tide per tidal day

• Spring tide -

How often do tides change?

• Tides usually change about four times each day, as Earth rotates beneath the pull of the Moon. An area having high tide has a low tide about 6 hours later. In about hours, the same area has a second high tide, followed about 6 hours later by another low tide.

High tide

Waves• Ocean waves transport energy, not water,

through matter or space. • When a wave passes, water particles end up in

the same places they began. • Wind passes energy to the water causing waves.

• In shallow water waves begin to feel the sea

bottom, causing them to lose speed. As the waves slow down, the wavelength shortens and the wave height increases.

• When a wave gets too tall, it begins to fall over on itself and then crashes onto shore.

Medium - a material through which a wave transfers energy

Compressional wave - matter vibrates in the same direction as the wave

travels

Transverse wave - the medium moves at right angles to the direction of the wave

Velocity= wavelength x frequency

• Earthquakes can produce three types of waves. One of these is a transverse wave called an S wave. A typical S wave travels at 5000m/s. Its wavelength is about 17 m. What is its frequency?

• A wave travels at a velocity of 4.0 m/s and has a frequency of 3.5 Hz. What is the wavelength?

S and P waves

• P wave is a primary wave - the fastest kind of seismic wave. Animals can hear the P waves of an earthquake. We may only feel the P wave. Also, known as compressional waves.

S waves are transverse waves the ground moves alternately to one side and then the other. They can only travel through solids.

Strike slip fault

Thrust fault

Plates

Converging and diverging bondaries

Parts of a transverse wave• The top of a transverse wave is called a

crest. The bottom portion is called the trough.

Amplitude and wavelength

Currents• Surface currents are set in motion by

wind and carry heat around the globe.

• El Nino is caused by a current.

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