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Tides

Tides. We experience tides on Earth when the ocean level rises and falls. We experience 2 high tides and 2 low tides in a little over one day. But what causes tides?. Tides and Gravity. The gravitational pull of the Moon is the most important reason we experience tides

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Tides

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  1. Tides • We experience tides on Earth when the ocean level rises and falls. • We experience 2 high tides and 2 low tides in a little over one day. • But what causes tides?

  2. Tides and Gravity • The gravitational pull of the Moon is the most important reason we experience tides • The Sun is also important. • Tides occur when the Earth gets “stretched” by the Moon’s gravity. • The parts of the Earth closest to the Moon get pulled more than parts in the opposite direction. • It is the difference in the strength of gravity with distance that causes tides.

  3. How Tides Work • Tidal forces are most noticeable when the object (or objects) being acted on is large (or far away from each other) • For example, you are too small to notice the tidal forces on your body • The oceans of the Earth, however, feel the effect of tidal forces from the Sun and Moon

  4. The Tides Caused by the Moon’s gravitational attraction on the water on Earth Excess gravity pulls water towards the moon on the near side But Forces are balanced at the center of the Earth Excess centripedal force pushes water away from the moon on the far side  2 tidal maxima  12-hour cycle

  5. The Tidal Bulge • Since water can flow more easily than rock it “piles up” into a bulge pointing towards the Moon and a bulge pointing away from the Moon. • The bulge on the side of Earth farthest from the Moon is due to the Earth being pulled “out from under” the water on the far side. • This varying amount of gravity is the “stretching force” that causes the tidal bulges to form along the Earth-Moon line.

  6. High Tide Low Tide

  7. Two Tides a Day • When we are beneath one of the tidal bulges we experience “high tide” • In the space between the bulges we experience “low tide” • The bulge (Moon) is moving very slowly!! 29.5 days for one Rev! • As the Earth spins beneath these tidal bulges we get carried into and then away from two high and low tides each day. We are spining through the bulge!! • Because the Moon moves in its orbit the tidal bulges move as well so it takes a little more than 12 hours for two high tides to occur.

  8. Spring Tides vs. Neap Tides • During each phase of the new moon and full moon the earth, sun, and moon come into alignment creating spring tides. When they are not in alignment neap tides occur. • Spring Tide- A tide which results in the greatest range between high and low tide • Neap Tide- A tide which results in the least tidal range between high and low tide

  9. Spring and Neap Tides But the Sun is also producing tidal effects, about half as strong as the Moon. Near Full and New Moon, The Moon and Sun’s gravity effects ADD up to cause spring (bigger high) tides. Spring tides Near first and third quarter, the Sun’s gravity effects work at a right angles to the moon’s, it weakens the effect of the moon’s gravity causing neap (smaller high) tides. Neap tides

  10. SO • There are two tidal bulges in the oceans • As the earth rotates, these bulges moves • Almost 2 high and 2 low tides per day • Strongest tides are near equator • Weakest tides are near poles

  11. Tidal Forces

  12. The Sun’s Role • Certainly the Sun contributes to tides as well but to a lesser degree. • When the Moon and the Sun are nearly aligned (that is at New Moon and Full Moon) the tidal forces are the strongest and we get more extreme high and low tides. These are called Spring Tides. • When the Moon is at 1st and 3rd Quarter the Earth experiences less extreme tides. These are called Neap Tides.

  13. Other Examples of Tides Tides are responsible for: • ripping interacting galaxies apart • pulling gas from one star to another in binary systems • and melting the interior of Io as it interacts with Jupiter and the other Galilean satellites.

  14. Other Cases of Tidal Forces • A black hole / neutron star / white dwarf pulling apart a companion star • Galaxies tearing each other apart

  15. Bay of Fundy • The Bay of Fundy is located on the west coast of Novia Scotia • It has the largest tidal range in the world of 53 ft. (16 m) • 100 billion tons of water flow into and out of the bay on and average tide. ~ creates strong rip currents, swirling whirlpools, and up-wellings. • The energy created by this great movement of water can be used as a clean renewable energy source. • Why is the tidal range so large at the Bay of Fundy?

  16. Summary questions • How does gravity cause tides? • What causes spring tides? • Why are there nearly two high tides a day? • What causes neap tides? • What causes the tides to move? The moon moving fast ot the earth rotating fast?

  17. Test Questions • Explain, with a diagram, how a neap tide is formed. • Show, with diagram, how two tides are formed in just over a day.

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