The pull of the moon

The pull of the moon

By Joseph Manso

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What is a tide, and what causes it to rise and fall?

Imagine that you are spending a relaxing day at the beach. You lie on

your towel and listen to the sound of the waves lapping the shore.

You doze off and awaken later to find yourself and your towel soaked in salty water.

You didn’t move any closer to the water in your sleep, so what happened?

The answer is simple. The tide came in. When you set your towel down

earlier, it was low tide. The tide came in while you were sleeping, which is

why you got wet. Tides are the rise and fall of ocean waters. There are

usually two high tides and two low tides every 24 hours. This means that

there is a span of about six hours between tides. The whole cycle repeats

about 50 minutes later each day. If you know that low tide happens at 9:00

one morning, it will happen around 9:50 the next day.

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Multiple Choice

Tides are.......................

• the rise and fall of ocean waters

• the rise and fall of lake waters

• the rise and fall of pond waters

Multiple Choice

If you know that low tide happens at 9:00

one morning, it will happen around ............the next day.

• 9:50

• 9:00

• 10:00

• 11:00

​You probably know that gravity is a force that pulls two objects together.

When you let go of a ball, it falls to the ground because of the pull of Earth’s

gravity. The moon also has gravity, and it is the moon’s gravity that causes

the rise and fall of tides. The moon pulls on the surface of the seas, which

causes them to bulge. At its highest point, this bulge or mound of water is

called high tide. The Earth rotates, or makes a complete turn, once every 24

hours. As Earth’s position changes, the same side of it no longer faces the

moon. When the moon’s gravity has the least effect on the oceans, low tide

takes place.

​The sun’s gravity also plays a role in the ocean tides. The sun isn’t as

close to Earth as the moon is, though, so it doesn’t have as great an effect.

When the sun, moon, and Earth all line up, a spring tide takes place. A

spring tide, which doesn’t have anything to do with the season, is a time of

very high and very low tides. When the sun and the moon do not line up, the

tides are not as high or as low. These are called neap tides.

Now that you know a little more about tides, you should be able to keep

yourself and your towel dry the next time you go to the beach!

Multiple Choice

What is Gravity?

• A force that makes us float

• An invisible force that keeps us on the ground

• An invisible force that rocks us

Multiple Choice

When the sun and the moon do not line up, the

tides are not as high or as low. These are called -------------

• neap tides.

• lead tides.

• neat tides.