The Breathing Sea: Why There Are Tides

Dominic Ashworth

Documentary

The Breathing Sea: Why There Are Tides

Dominic Ashworth

Writr

Chapter 1

Two Bulges

Stand on a beach for a day and the sea will come to meet you and then back away again. On most coasts it does this twice, with a high tide roughly every twelve and a half hours. The schoolbook explanation is that the Moon pulls the water. That is true, and also not quite the whole story, because the Moon's pull on its own would give you one high tide a day, not two.

Dominic Ashworth

Start with the Moon. Its gravity reaches across the gap and tugs at everything on Earth, water included. The ocean on the side facing the Moon is pulled slightly more strongly than the solid Earth beneath it, because it is closer, and so it heaps up very gently towards the Moon. That is the first bulge.

The Breathing Sea: Why There Are Tides

The second bulge is the part that takes a moment. The ocean on the far side of the Earth is further from the Moon than the solid Earth is, so it is pulled slightly less. The Earth, in effect, is drawn away from that far-side water a little more than the water is drawn along with it, and the water is left behind as a second heap, pointing away from the Moon. The two bulges sit on opposite sides of the planet, on a line running through the Moon.

Dominic Ashworth

The Earth then turns underneath them. Once every day, each point on a coast is carried through a bulge, then through the low between, then through the other bulge, then another low. Two highs, two lows. Because the Moon is itself moving around the Earth, in the same direction the Earth spins, each place has to turn a little further every day to catch up with the bulge, which is why the tides arrive about fifty minutes later each day rather than keeping to the clock.

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Chapter book · Adult

The Breathing Sea: Why There Are Tides

Name: The Breathing Sea: Why There Are Tides
Price: 6 AUD
Rating: 5 (1 reviews)
Author: Dominic Ashworth

by Dominic Ashworth

51 reviewRated adult

Twice a day, on most coasts, the sea comes in and goes out again. The reasons are stranger and more beautiful than the schoolbook version, and this short documentary walks through them one at a time.

documentary
non-fiction
ocean
science

6 credits (A$6.00)

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Reviews

Lena
Read it on the sand at low tide, which is the right way. Clear, careful and quietly moving at the end.