Question: Why is there tides in the sea?

Luke Williams answered on 11 Mar 2018:

This is the effect of the moon. In fact, there are a number of different forces at work here, as the moon orbits the Earth, the Earth rotates and the water gets pushed and pulled all over the place. This is why we have tides – the water keeps trying to catch up with the moon, but it never reaches it.

To start with, wherever the moon is, it attracts the water to come a little closer to it. This is caused by gravity. Because of the size of Earth, this ends up stretching the planet a little bit, which doesn’t really affect the solid part, but to liquid, there is a bigger effect.

If you watch the moon through a month, it will go from new moon to full moon and back – this is because the different position of the sun and moon lights up different parts of the moon. These different positions have different effects on the tide. There are other effects caused by how high the moon is in the sky too – again, all to do with where exactly the moon is. Similarly the moon also gets a bit closer and further from Earth, this also changes things a bit.

So to sum up – where the moon is, is where the sea wants to be. Because the moon keeps moving, the sea never stops following!