Science
How do the tides work?
The tides work mainly because of the Moon's gravity pulling on Earth's oceans. The Moon tugs the water toward it, creating a bulge, while another bulge forms on the opposite side — so most coasts get two high tides and two low tides each day.
See it in motion.
Watch a 2-minute animated lesson that shows exactly how the tides works.
Step by step
- 1The Moon's gravity pulls hardest on the ocean nearest it, raising a bulge.
- 2A second bulge forms on the far side, where the pull is weakest.
- 3As Earth rotates, coasts pass through these bulges, giving high and low tides.
- 4The Sun's gravity adds to the effect, strengthening tides at new and full moons.
- 5Most places get two highs and two lows roughly every 24 hours.
Frequently asked questions
- Why are there two high tides a day?
- The Moon raises one ocean bulge facing it and another on the opposite side, so Earth's rotation carries each coast through two highs daily.
- Does the Sun affect tides?
- Yes. When the Sun and Moon line up (new and full moons), their combined pull creates extra-large 'spring' tides.
- Why isn't high tide at the same time each day?
- The Moon moves along its orbit as Earth spins, so the tidal cycle shifts about 50 minutes later each day.