The Earth and the moon are attracted to each other like magnets. This is called a tractive force. The moon is constantly trying to pull the Earth closer. But despite the moon´s efforts, the Earth remains steadfast, and the water is the only thing that gets pulled, because it is constantly in motion. Depending on where the moon is in relation to the Earth, the ocean water gets pulled in that direction, creating a bulge. The bulge then makes the sea level higher on the side of the Earth that faces the moon. The sea level drops on the side of the Earth that's facing away from the moon. This is the dynamic that creates the tides. The moon produces a semidiurnal tide every 12 hours and 25 minutes and a diurnal tide every 24 hours and 50 minutes.
The sun also participates in making tides. However, the moon has a much stronger gravitational pull than the sun because the sun is farther away from the Earth. The sun's gravitational pull on the Earth is only about 40 percent that of the moon's. Like the moon, the sun produces semidiurnal and diurnal tides, only that its rotation is not as long. It produces a semidiurnal tide every 12 hours and a diurnal tide every 24 hours. Because the Earth is constantly moving, different oceans experience different solar and lunar tides. Diurnal tides, one high and one low, occur mostly in the Gulf of Mexico and Southeast Asia. Semidiurnal tides, two high and two low, occur mostly in the Atlantic Coast of the United States and Europe.
When the sun and the moon are aligned with the Earth, the gravitational pull is unusually strong, and very high tides and very low tides are created. The moon revolves around the Earth, and together they orbit the sun. The sun, Earth and moon have to be in a certain position for spring tides to occur. Both the moon and the sun have to be on the same side of the Earth, or they have to be on opposite sides of the Earth. This happens when there is a full moon and a new moon, about every 14 to 15 days.
Neap tides occur during quarter moons. Neap tides are much weaker than spring tides, because the sun and the moon are perpendicular to the Earth, and their gravitational forces cause the bulges to cancel each other out, creating a low tide that is not very low and a high tide that is not very high.