Gravitational Phenomenon Explained

The question asks to identify a phenomenon explained by the universal law of gravitation, which arises from the combined and differential gravitational forces exerted by the Moon and the Sun on the Earth.

Analyzing the Options

• The centripetal force: While gravity provides the centripetal force for celestial orbits, this option doesn't specifically describe a phenomenon caused by the differential pull of the Moon and Sun on Earth itself.
• The motion of planets around the Sun: This is explained by gravitation, but the question emphasizes the Moon and Sun's specific influence on Earth, suggesting a more localized effect.
• The occurrence of ocean tides: Tides are a direct result of the differential gravitational forces from the Moon and Sun. These forces pull harder on the side of Earth closer to them and weaker on the farther side, creating bulges in the oceans.
• The decrease in the value of g from poles to equator: This variation is primarily due to the Earth's rotation (centrifugal effect) and its oblate shape, not directly the combined gravitational pull of the Moon and Sun.

Identifying the Correct Phenomenon

Ocean tides are the most fitting explanation. The universal law of gravitation states that every particle attracts every other particle. The Moon's gravitational pull is strongest on the side of Earth facing it, pulling the water into a bulge. On the opposite side, the Moon pulls the Earth more strongly than the water, effectively leaving the water behind and forming another bulge. The Sun exerts a similar, but weaker, effect due to its greater distance. The combination and difference in these pulls cause the regular rise and fall of sea levels known as tides.