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Name: Erin Sterner
Status: Student
Age: 9
Location: N/A
Country: N/A
Date: N/A 

We are studying the ocean now. Can you explain to me how tides work?

Hi Erin,
Thanks for your question.

Any large object has gravity. We know that the earth has gravity because when we jump we get pulled toward the earth.

The moon is also a large object and it has gravity. If you jump on the moon (as Neil Armstrong and Buzz Aldrin did) you would get pulled back toward the moon.

People are not the only things pulled toward large objects by gravity. They also pull other large objects. The earth pulls the moon toward the earth. The moon also pulls the earth toward the moon. Because the two objects are pulling on each other the moon orbits the earth rather than flying off into space.

When the moon pulls on the earth it doesn't just pull the earth as a whole. Every little bit of the earth is pulled toward the moon. Solid things can't respond to the moon's gravity pull very easily since they are stuck in place.

However the sea is liquid and is free to move. The sea is pulled toward the moon and as the sea moves toward the moon it becomes slightly higher on one side of the earth. Then the earth turns and the moon is on the other side of the planet. Now the reverse happens and the sea becomes higher in a new place. The high tide travels around the earth with the moon.

The same thing happens in a glass of water but the effect is so small that you could not possibly notice it. It is only when you get huge amounts of water, as you do in the sea, that the effect of the moon's pull becomes noticeable.

I hope this answers your question.

Cameron Millsom

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