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Tides
Intermediate
The Moon's gravity gradient stretches Earth's oceans.
The Moon's gravity is stronger on the near side of Earth than the far side; this difference (gradient) stretches the oceans into two bulges, giving two high tides per day. The Sun adds spring and neap effects.
Tidal range ≈ 1 m in the open ocean.
Tides come from differences in gravity, not gravity alone.
In more detail
Tides are caused by differences in gravitational pull across Earth, mainly from the Moon and the Sun. The pull is stronger on the near side, stretching the oceans into two bulges.
Real-world uses
- Tide tables are used by sailors and harbour operators.
- Coastal power schemes can harness tidal energy.
- Coastal engineers and sailors plan for the tides, which are caused by the Moon and Sun pulling unevenly on Earth's oceans.
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Frequently asked questions
Why are there two high tides a day?
Because the Moon's tidal bulges occur on both sides of Earth.
Does the Sun cause tides too?
Yes, the Sun causes tides about half as strong as the Moon's.
Why are there two high tides a day?
The Moon pulls the water on both sides of Earth, creating two bulges that move around the planet as it spins.
Related topics in Gravitation & Orbits
Perihelion and aphelion · Orbital transfers · Gravity assist · Tidal locking · Roche limit · Lagrange points