Secrets of the tides

At any coast, the tide flows up and down, in and out. But WHY?

How Tides Work

Tides happen because of the Moon –but it’s complicated!

1. The Moon is smaller than the Earth, but it still has gravity . It pulls on the Earth’s water, making it ‘bulge’ towards the Moon.

spins once a day, so different parts of the sea move into the bulge areas. They rise up, high tide !

Times Of The Tides

The Moon’s gravity causes tides.

2. The Moon also pulls the Earth, making it swing around slightly as the Moon orbits it. This makes water bulge out on the side opposite the Moon too!

But wait… it gets even weirder! The tide goes in and out roughly twice a day – but not exactly…

The Earth spins, moving through two high tides a day.

But at the same time, the Moon orbits the Earth, about once every 28 days.

This means the bulges change position, gradually moving around the world.

So it actually takes a bit more than 24 hours for the tide to go in and out twice. Each day, high tide happens a bit later than the day before.

What did the beach say when the tide came in? Long time no sea!

Tide

Tides happen at different times every day, and that can be annoying! Imagine going to the beach to build sandcastles... but when you get there, it’s high tide and the

HOLD BACK THE TIDE!

You can’t stop the tide… or CAN you? To protect the coastline from erosion, different kinds are used.

Tide Machines

Sand can even be shipped in to page 34.

Tidal Islands

It’s an island! Oh no it isn’t! Tidal islands are only islands sometimes. They’re cut off by the sea at high tide, but at low tide, they’re linked to the mainland by a beach or a path called a causeway

St Michael’s Mount in Cornwall is a tidal island

Today, we use computer software to predict the tides. But 150 years ago, they used amazing tide-predicting machines like this. They had lots of cogs and wheels to work out the tide cycles and were an early type of computer!

need to protect them! Build a wall around them using tightly packed sand, pebbles, seaweed, driftwood or any other natural materials from the beach.

3. What happens when the tide comes in? Which materials keep the water away for the longest

If you can’t get to a real beach, you could use play sand to make your own miniature beach in a dish, tray or sandpit. Build a mini sandcastle and sea wall, then add more and more water to make a rising tide. You can mimic waves by pushing on the water with a plastic bottle or cup.