How do tides occur?

• A. Wind on the oceans.
• B. Gravitational pull of the moon and sun on Earth's oceans.
• C. Rotation of Earth.
• D. Tectonic activity.

Answer: (B)

Tides come from gravity pulling on ocean water. The Moon’s gravity tugs on the oceans, pulling more strongly on the side of Earth that’s closest to the Moon and less strongly on the far side, generating a bulge on both sides of the planet. The Sun does the same, though its gravity is weaker because it’s so far away. These gravitational pulls create two large bulges that stay roughly aligned with the Moon–Sun line. As Earth rotates, coastlines move under these bulges, causing the regular rise and fall of sea level we feel as tides.

When the Sun and Moon pull in the same direction, their effects add up, producing higher high tides and lower low tides—spring tides. When they are at right angles in the sky, their forces partially cancel, giving lower high tides and higher low tides—neap tides.

Other processes like wind can generate waves and local water movement, but the regular tides are driven by the Moon’s and Sun’s gravity. Earth’s rotation influences the timing of when tides occur at a given location, while tectonic activity can change local sea level but doesn’t cause the regular tidal cycle.