# Tides Demonstration

Stage 1

### The strength of the Moon's gravitational pull varies across the Earth.

The orange arrows in the diagram show the strength of the Moon's gravitational force across the Earth. The length of the arrows tells you how strong it is. The longer the arrow, the stronger the Moon's gravitational pull. Remember the Earth is constantly spinning on its axis.

The arrows show the force is the strongest on the surface of the Earth facing towards the Moon. It is weaker at the centre of the Earth. It is the weakest at the surface of the Earth facing away from the Moon.

Stage 2

### The tidal force also varies across the Earth.

It is the difference in the forces at the surface and centre of the Earth that causes the tides. We call this 'tidal force'. The blue arrows in the diagram show where there is a tidal force and the direction it is acting. You can see a tidal force on the surface of the Earth facing towards the Moon. But there is also a tidal force on the opposite side of the Earth, on the surface facing away the Moon.

Stage 3

### Water flows towards the peaks of the tidal force.

The tidal force is not strong enough to change the solid rock in the Earth. But the tidal force is strong enough to move liquid water. The water in the Earth's oceans flows to form a bulge where the tidal force is strongest. The result is two bulges on opposite sides of the Earth. We get two tides each day because the Earth is always spinning. We get one high tide when our part of the Earth turns through the bulge nearest the Moon. And we get another high tide when our part of the Earth turns through the bulge furthest from the Moon.

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