What are tides?
Quick answer from Eartha
Tides are when the sea rises up the beach and then falls back again, twice a day. This happens because the moon's gravity gently pulls on the ocean, like an invisible tug. When the pull is strongest, we get high tide. When it's weaker, we get low tide.
The longer story
Tides are the regular rise and fall of sea level along the coast. Most beaches around Australia experience two high tides and two low tides roughly every 24 hours.
The main cause is the moon's gravity. Even though the moon is far away, its gravity is strong enough to pull the ocean's water slightly towards it, creating a bulge of higher water on the side of Earth facing the moon.
The sun's gravity also plays a smaller part. When the sun, moon and Earth line up during a full or new moon, their pulls combine to create extra-high spring tides. When they're at right angles, we get smaller neap tides.
Tides matter for many reasons. Fishers and sailors plan trips around them, rock pool creatures rely on the changing water, and knowing the tide times helps keep swimmers and surfers safe at the beach.
Try this at home: Track a tide at the beach
- Next time you're at the beach, place a stick or stone at the water's edge.
- Come back after an hour and see how far the water has moved.
- Talk about whether the tide is coming in or going out.
Words to know
- Gravity
- An invisible force that pulls objects towards each other.
- High tide
- When the sea rises highest up the beach.
- Low tide
- When the sea pulls back and the beach is at its widest.
For grown-ups: what is my child learning here?
Age band: 8-11
Curriculum link: Australian Curriculum v9 Science, AC9S5U01 - Earth and space, gravity
The concept: Connects the moon's gravity to a visible, everyday coastal phenomenon.
More classroom ideas are on our teachers page, and safety notes for families are on for parents.
Last reviewed: · How we check answers
More questions kids ask
Got a nature question of your own?
Ask Eartha your own question →