Tides

Kim and Philip are having a great time at the beach. - Look Philip, the sea level has gone down! You must bury me in the sand, so you can only see my head! - It’s so much fun to be buried in the sand! - Um, Kim, you need to be careful, the sea is getting closer and closer to you. - Oh no, help me out Philip! Philip and Kim forgot that it’s not a great idea to bury someone in the sand so close to the sea, because the sea level rises and falls twice a day. The rising of the sea level is called FLOW, and the falling is called EBB. These are the two phases of a phenomenon we call TIDES.

Tides happen because of the interactions between the Earth, the Moon and the Sun. But how? First, we need to know that all things with mass are pulled towards each other, because of the gravitational force. The Earth has a big gravitational force, and this is the reason why everything on Earth, stays on Earth and doesn’t float up into space. The Moon also has a gravitational force, and it pulls the Earth and things on it towards itself.

While on land we don’t really feel it, the water in the sea is much more responsive to this force. The water is pulled towards the moon, creating a bulge on the side of the Earth that is closest to the Moon. This bulge means high sea levels or HIGH TIDE on that side of the Earth. The Moon also attracts the Earth, so the Earth gets a little bit closer to the Moon. The seas on the side of the Earth furthest away from the Moon aren’t pulled as much.

This creates another HIGH TIDE on that side of the Earth. At right angles to the areas with high tides, the water doesn’t bulge, so the tide is low. Because the Earth rotates, every place on the Earth’s surface passes through the areas of high and low tide twice a day. So now we know how the Moon and the Earth affect the tide, but what about the Sun? The Sun also has a gravitational force that pulls the Earth and everything on it, but it’s weaker than that of the Moon.

When we have a full or a new Moon, the Sun’s gravitational force will pull in the same line as that of the Moon. This will cause the water to bulge out even more, causing higher tides, or as we call them, SPRING TIDES. Whenever the Sun, the Earth and the Moon are not aligned, the Sun and the Moon will pull the water in different directions. When the Sun and the Moon are at right angles, their forces cancel each other out, and that’s when tides are the lowest. We call them NEAP TIDES.

The forces of the Earth, the Moon and the Sun affect water all across the world. But the tides are most noticeable on the coast - like on this beach where Kim and Philip are!