Tides

Essential Question:

What causes tides in the oceans?

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

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

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

Earth

Moon

Sun

High TideHigh Tide

Low Tide

Low Tide

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).

So, as the Earth spins around its axis, how many high and low tides do we have a day?

Bay of Fundy

The Bay of Fundy in Canada is noted for the

great differences between its high and low tides.

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.

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

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