Science · For ages 7–11
How Tides Work for kids, explained simply
Tides are the slow rise and fall of the sea. They happen mainly because of the Moon’s gravity, which gently pulls on Earth’s oceans. This pull stretches the water into two bulges — one on the side facing the Moon and one on the far side. As Earth spins through these bulges each day, most coasts get two high tides and two low tides.
The big ideas
The Moon’s gravity pulls the oceans
Gravity is the pull that every object has on every other object. The Moon is large and close enough that its gravity tugs on Earth’s water, lifting the ocean into a bulge on the side of Earth nearest the Moon. The Sun pulls on the oceans too, but because it’s so far away, its effect on tides is smaller than the Moon’s.
There are TWO bulges — one near, one far
Here’s the surprising part: there’s a bulge of water on the side facing the Moon AND a second bulge on the opposite, far side of Earth. This happens because the Moon pulls the near ocean hardest, the solid Earth in the middle less, and the far ocean least of all — so the far ocean is, in effect, left behind in a bulge. As Earth spins through both bulges, most coasts get two high tides every day.
Spring and neap tides
When the Sun and Moon line up (at a new Moon or full Moon), their pulls add together to make extra-big "spring" tides. When the Sun and Moon are at right angles, their pulls partly cancel, giving gentler "neap" tides. So the size of the tide changes with the pattern of the Sun and Moon in the sky.
A quick quiz
1. What mainly causes the tides?
Choices: The wind blowing the sea · The Moon’s gravity pulling on the oceans · Fish moving the water
Answer: The Moon’s gravity pulling on the oceans. Tides are caused mainly by the Moon’s gravity gently pulling Earth’s oceans into bulges. The Sun helps too, but its effect is smaller because it’s so far away.
2. How many tidal bulges of water are there, and where?
Choices: One, only on the side facing the Moon · Two — one on the side facing the Moon and one on the far side · Three, spread around the Earth
Answer: Two — one on the side facing the Moon and one on the far side. There are two bulges: one facing the Moon and one on the opposite side. The Moon pulls the near ocean, the solid Earth, and the far ocean by different amounts — which leaves the far ocean bulging out too. That’s why most coasts get two high tides a day.
3. When do we get the biggest "spring" tides?
Choices: When the Sun and Moon line up together · When the Moon is hidden behind clouds · Only in springtime
Answer: When the Sun and Moon line up together. When the Sun and Moon line up, their gravity pulls in the same direction and adds together, making extra-big spring tides. Despite the name, they happen all year round — not just in spring.
For parents: helping your child think about how tides work
Tides are a perfect topic for stretching a child’s imagination beyond Earth, because the cause is in the sky. The most engaging opening is a puzzle: "Why does the sea move up and down the beach every day — what could possibly be strong enough to lift a whole ocean?" Let them guess before revealing the answer: the Moon’s gravity, reaching across nearly 400,000 kilometres of space. That fact alone is wonderful — something so far away gently tugs our seas. The trickiest and most important idea to get right is that there are two bulges, not one. Most people assume the ocean only bulges toward the Moon, but there’s an equal bulge on the far side too. A gentle way to picture it: the Moon pulls the near water hardest, the solid Earth in the middle a bit less, and the far water least — so the far ocean is, in a sense, left behind, bulging outward. This is why most coasts get two high tides each day, not one. Avoid the tempting shortcut of saying only the Moon-facing side rises; the two-bulge picture is the accurate one. If you live near the sea, look up a tide timetable together and watch a prediction come true — there’s real magic in forecasting the ocean from the position of the Moon. Ask your child to explain, in their own words, why there are two high tides a day and not just one.
Frequently asked questions
How do tides work?
Tides are caused mainly by the Moon’s gravity, which pulls Earth’s oceans into two bulges — one on the side facing the Moon and one on the far side. As Earth spins through these bulges, most coasts experience two high tides and two low tides each day. The Sun adds a smaller effect.
Why are there two high tides a day instead of one?
Because there are two bulges of water, not one. The Moon pulls the near ocean hardest, the solid Earth less, and the far ocean least — which leaves the far ocean bulging out as well. As Earth rotates through both bulges, each coast passes through two high tides a day.
Does the Sun affect the tides too?
Yes, but less than the Moon, because the Sun is much farther away. When the Sun and Moon line up, their pulls combine to make large "spring" tides; when they sit at right angles, the pulls partly cancel, giving gentler "neap" tides.
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