1. Essential Question: What causes tides in the oceans?

2. What are Tides?
The daily rise and fall of Earth’s waters on its coastlines are called tides.
As the tide comes in, the level of water on the beach gradually rises
As the tide goes out, water flows back to the sea
Unlike surface waters, tides happen regularly no matter how the wind blows.
Tides occur in all bodies of water, but are most noticeable in the oceans and large lakes

3. What causes Tides?
Tides are caused by the interaction of Earth, the moon, and the sun
How?
Gravity!
Gravity is the force exerted by an object that pulls other objects toward it.
As the distance between objects increases, the pull of its gravity weakens

4. What causes Tides?
The moon pulls on the water on the side of Earth closest to it more strongly that it pulls on the center of Earth
This pull creates a bulge of water called a tidal bulge on the side of Earth facing the moon.
The water farthest from the moon is “left behind”, forming a second bulge

5. Tides are more influenced by the gravitational effect of the Moon than they are by that of the Sun (the Moon's closeness to us outweighs by far the Sun's greater size).
Low Tide
Moon
Earth
High Tide
High Tide
So, as the Earth spins around its axis, how many high and low tides do we have a day?
Low Tide
Sun

6. Bay of Fundy
The Bay of Fundy in Canada is noted for the great differences between its high and low tides.

7. How does the Sun affect Tides?
The Sun also causes tides on the Earth, but they are smaller than the Lunar tides.
When the Moon and Sun are aligned, their tidal forces combine, and the resulting tides are largest.

8. What are Spring Tides?
Twice a month, at the new moon and the full moon, the sun and the moon are lined up,
Their combined gravitational pull produces the greatest difference between the heights of the tides
Results: Higher High Tide and Lower Low Tide

9. What are Neap Tides?
When the sun and the moon are at right angles to each other it produces a neap tide
This acts to “even out” the water level over Earth’s surface decreasing the difference between high tide and low tide
Results: Lowest High Tide and Highest Low Tide