1. I Can Explain how the moon’s gravity causes tides on Earth
Summarize the predictable pattern of tides

2. What Causes Tides?

3. Beach
Have you spent a day on an ocean beach and noticed that the water comes in closer or goes out farther during the day? Have you wondered why the water does this?

4. Video Clip http://studyjams. scholastic

5. What Are Tides?
Tides are the daily rise and fall of Earth’s waters on its coastlines. There are two high tides and two low tides in a little less than 25 hours—just a little more than one full day.

6. Rainwater filled up the sea.
You arrive at the beach at 9:00 A.M. You lay a towel on the sand, and then you run 30 steps to reach the water’s edge. By 3:00 P.M., the water has almost reached your towel. What do you think happened?
The waves got bigger.
Rainwater filled up the sea.
The tide came in.

7. Rainwater filled up the sea.
You arrive at the beach at 9:00 A.M. You lay a towel on the sand, and then you run 30 steps to reach the water’s edge. By 3:00 P.M., the water has almost reached your towel. What do you think happened?
The waves got bigger.
Rainwater filled up the sea.
The tide came in.

8. What Causes Tides?
Tides are caused by the interaction of Earth, the Moon, and the Sun.
Gravity is the reason for tides.
Gravity is the force exerted by an object that pulls other objects toward it.

9. Moon’s Gravity and Tides
The Moon’s gravity affects the water on Earth’s surface.
Since the Moon is close to the Earth, it has a strong gravitational pull on it (closer objects have stronger gravitational pull).

10. Moon’s Gravity – Tidal Bulges
The Moon pulls on the water on the side nearest to it more strongly than it pulls on the center of the Earth.
This pull creates a bulge of water, called a tidal bulge, on the side Earth facing the the the Moon.

11. Moon’s Gravity – Tidal Bulges
The water on the side of Earth facing away from the Moon has a less strong pull.
This water is “left behind” and forms a second bulge.
As Earth rotates, different places on the planet’s surface pass through the areas of the tidal bulges and have the change in water levels.

12. QUICK CHECK

13. On Saturday at the beach, the water is highest at 11:15 A.M.
On Sunday, the water is highest at 11:55 A.M. Why does the tide come in later?
It’s really the same time, but your watch is fast, so you think it’s earlier.
The moon has moved a little, so the beach is closest to the moon at a later time.
The tide always comes in later on Sunday.

14. On Saturday at the beach, the water is highest at 11:15 A.M.
On Sunday, the water is highest at 11:55 A.M. Why does the tide come in later?
It’s really the same time, but your watch is fast, so you think it’s earlier.
The moon has moved a little, so the beach is closest to the moon at a later time.
The tide always comes in later on Sunday.

15. Tidal Bulges – High Tide
In places where there are tidal bulges, high tide is occurring along the coastlines.
High
Tide
High
Tide

16. Tidal Bulges – Low Tide
In places between the bulges, low tide is occurring.
LOW TIDE
LOW TIDE

17. Sun’s Gravity and Tides
The Sun is so large that its gravity also affects tides.
At times, the Sun and Moon pull together on Earth’s waters in the same direction.
At other times they pull in different directions.

18. Daily Tide Cycle
Seashores have four tides every day – two high tides and two low tides.
A change from low to high tide or vice versa takes about hours and 12 minutes.

19. Monthly Tide Cycle
Changes in the positions of Earth, the Moon, and Sun affect the height of tides during a month.

20. QUICK CHECK

21. Spring Tides
Spring tides occur 2 times a month, during a full and new moon when the Earth, Sun, and Moon are lined up.

22. Neap Tides
Neap tides occur in between spring tides, at the first and third quarters of the Moon when the Sun and Moon pull at right angles to each other.

24. The sun is rising, but you can still see the moon in the western sky
The sun is rising, but you can still see the moon in the western sky. Would you expect the tide to be going out?

25. The sun is rising, but you can still see the moon in the western sky
The sun is rising, but you can still see the moon in the western sky. Would you expect the tide to be going out?

26. Are there any Practical Use for Tides?

27. You’re on the beach at midnight. The moon is right overhead
You’re on the beach at midnight. The moon is right overhead. Will the tide be…
…high, because the moon is as close as it can be to where you are?
…between low and high, because the tide rises and sets with the Sun?
…low, because the tide is caused by the Sun’s gravity?

28. Writing Assignment
Write about an experience you've had where you've seen tides. It could be in an estuary, on a shoreline beach, or in a river affected by tides. What did you notice? If you've never been someplace to see a tide, write about what you think you would see as the tide came in or went out.
Illustrate your writing