1. Tides

2. Gravity Gravity is an invisible force of attraction between all objects. The size of the force depends on the mass of the object. What celestial object is attracted to the Earth? The Moon What celestial object is the Earth attracted to? The Sun The study of tides starts with:

3. How does the Moon effect Earth? The Moon’s gravity pulls on the Earth, but because the Earth is solid, it doesn’t seem to respond. However, the Earth is mostly covered with water. Water is a liquid and does respond to the pull of the Moon. This response creates tides.

4. Tides The how and why of tide formation is very complex. This presentation will try to simplify how and why tides form. To do this….

5. Imagine that there is nothing but water covering the Earth.

6. Now, imagine looking at the Earth from above the North Pole. N

7. Let’s add the moon to this system. N

8. The moon pulls on the water. This creates a bulge. N

9. But because the Earth is spinning, there are actually 2 bulges created. You’ll learn more about this in Physics. N

10. This bulge of water follows the moon as it orbits the Earth. N

11. It takes the moon about 28 days to revolve around the Earth. N

12. This makes the times that the tides occur change in a predictable pattern.

13. But there is more going on than just the revolution of the moon around the Earth. The Earth rotates every day. N N

14. Let’s put a person on the equator of the Earth. Remember, you are looking at the Earth from the North Pole, so this person appears to be on the edge of the Earth. N

15. As the Earth rotates, the person will move through two very high bulges of water and two areas of low water each day. N

16. We call these areas high tide and low tide. Remember, in a 24 hour period of rotation, there are two high tides and two low tides. N

17. This is what it looks like with both motions. N

18. Spring Tides Tides that occur when the sun and moon are directly in line with the earth and their gravitational pulls reinforce each other. Produces the highest high tides and the lowest low tides This occurs during the full moon and new moon. High Tide N

19. Neap Tides a tide just after the first or third quarters of the moon when there is the least difference between high and low water N High Tide Low Tide

20. Why does the Earth experience tides? (The gravitational attraction of the Moon on the water of the Earth. The water bulges toward the Moon, creating a high tide.) How do high and low tides occur? (The gravity from the Moon pulls on the water causing a bulge, and the Earth itself is also pulled in that direction, creating a bulge on the opposite side. The areas in between the bulges are the low tides.)

21. How do spring and neap tides differ? (When the Earth, Moon, and Sun are in a straight line, the gravitational attraction is at its greatest because of the additive property of gravity. This causes a larger bulge of water. When the Earth, Moon, and Sun are in a perpendicular configuration, the gravitational attraction of the Moon pulls counter to the Sun. This causes a lower than normal bulge of water. There are only two neaps and two springs in a month.) How often do tides occur? (Typically, there are two highs and two lows per day, every six hours.)