The theory of gravitation can be used to explain the tides. The gravitational pull of the Moon is the main reason for the tides on Earth. The Moon attracts the water in the seas, pulling up a bulge of water towards it. The Earth itself is also attracted and so another bulge of water is ‘left behind’ on the opposite side of the Earth from the Moon. Places on the Earth beneath the two bulges have high tides at that moment while places at right angles to these have low tides at that moment.
The Earth rotates beneath these two bulges and as it does so every place on Earth has two high tides and two low tides a day. The size of the tidal bulges has been exaggerated and the distance between the Earth and the Moon is proportionally much greater than that shown in the animation.