Final answer:
Tides on Earth are primarily caused by the Moon's gravitational pull, which exerts differential forces on Earth's oceans, creating two tidal bulges that Earth rotates through daily. The Sun's gravitational force also contributes, but to a lesser extent.
Step-by-step explanation:
The most prominent force inducing tides on Earth is the Moon's gravitational pull. While the Sun does exert a significant tidal force due to its gravitational attraction, the tidal effect of the Sun is less than that of the Moon. This is because of the differential forces caused by the Moon's gravitational pull on different parts of the Earth. The Earth and its oceans are stretched into an oblate spheroid shape, with high tides occurring on both the side of Earth nearest the Moon and the opposite side.
Lunar tides are observable as the sea level rises and falls about twice per day, which is a result of Earth rotating through two tidal bulges caused by the Moon's gravity. The Sun also contributes to the tidal effects, especially when its position relative to the Earth and Moon is such that the forces from both bodies align, amplifying the net tidal effect.