Chapter 11 S3Chapter 11 S3

TidesTides

Ch 11 S3 Essential Ch 11 S3 Essential QuestionsQuestions

1.1.What causes What causes tides?tides?

2.2.What affects the What affects the heights of tides?heights of tides?

3.3.How are tides a How are tides a source of energy?source of energy?

What Causes Tides?What Causes Tides? Tides are caused by the Tides are caused by the interaction of Earth, the interaction of Earth, the moon, and the sun.moon, and the sun.

Tides are the daily rise Tides are the daily rise and fall of Earth’s and fall of Earth’s waters on its coastlines.waters on its coastlines.

As a tide comes in, the As a tide comes in, the level of water rises. High level of water rises. High tide is when the water is tide is when the water is highest. Then the tide highest. Then the tide flows out, flowing back flows out, flowing back toward the sea. Low tide toward the sea. Low tide is when the water reaches is when the water reaches its lowest point.its lowest point.

Gravity causes tides. Gravity causes tides. Gravity is the force an Gravity is the force an object has that pulls other object has that pulls other objects toward it.objects toward it.

The moon’s gravity pulls The moon’s gravity pulls on Earth’s waters. The on Earth’s waters. The moon’s gravity creates a moon’s gravity creates a bulge of water on the bulge of water on the side of Earth closest to side of Earth closest to the moon. The water on the moon. The water on the other side of Earth the other side of Earth forms a second bulge. forms a second bulge. These are called tidal These are called tidal bulges. In places where bulges. In places where there are tidal bulges, there are tidal bulges, high tide occurs.high tide occurs.

In many places, there are In many places, there are two high tides and two two high tides and two low tides each day. In low tides each day. In other places, one set of other places, one set of tides is so small that it tides is so small that it seems like there is only seems like there is only one high tide and one low one high tide and one low tide per day.tide per day.

Look on page 368 for Look on page 368 for question #5, #6, and #7question #5, #6, and #7

Changes in the positions Changes in the positions of Earth, the moon, and of Earth, the moon, and the sun affect the the sun affect the heights of the tides heights of the tides during a month.during a month.

The sun’s gravity also The sun’s gravity also affects Earth’s tides. affects Earth’s tides. The sun pulls the water The sun pulls the water on Earth’s surface on Earth’s surface toward it.toward it.

When the sun and When the sun and the moon are lined the moon are lined up, their gravities up, their gravities combine to produce a combine to produce a spring tide. A spring spring tide. A spring tide is a tide with the tide is a tide with the greatest difference greatest difference between high tide between high tide and low tide.and low tide.

When the sun and the moon When the sun and the moon are at right angles to each are at right angles to each other, the sun’s gravity pulls other, the sun’s gravity pulls some water away from tidal some water away from tidal bulges. The result is a neap bulges. The result is a neap tide. A neap tide is a tide tide. A neap tide is a tide with the least difference with the least difference between high tide and low between high tide and low tide.tide.

Look on page 368 and 370 for Look on page 368 and 370 for questions #10 and #11questions #10 and #11

The movement The movement of huge amounts of huge amounts of water between of water between high and low tide high and low tide is a source of is a source of potential energypotential energy—energy that is —energy that is stored and can stored and can be used.be used.

A lot of water moves A lot of water moves between high and between high and low tides. In some low tides. In some places, tidal power places, tidal power plants use the plants use the energy of tides to energy of tides to produce electricity.produce electricity.

Look on page 370 for Look on page 370 for questions #13 & #14questions #13 & #14

The energy of tides The energy of tides is used only in places is used only in places where there is a big where there is a big difference between difference between high tide and low high tide and low tide. There are very tide. There are very few places in the few places in the world with such a big world with such a big difference.difference.

Ch 11 S3 Essential Ch 11 S3 Essential QuestionsQuestions

1.1.What causes tides?What causes tides?

2.2.What affects the What affects the heights of tides?heights of tides?

3.3.How are tides a How are tides a source of energy?source of energy?