Why the Ocean Moves: Waves and Tides
Put your toes in the sand at the beach and wait. In a few seconds, cold water rushes up and touches your feet, then pulls back out again. A little while later, it happens again — but bigger! The ocean is never still. It moves in waves that crash every few seconds, and it moves in tides that rise and fall over many hours.
What You'll Learn
- What makes ocean waves - Why the ocean rises and falls in tides - What high tide and low tide look like on a beach - How the Moon controls the tides
What Makes a Wave?
Wind blowing over the ocean pushes the water into wave shapes. The stronger the wind, the bigger the wave. A gentle breeze makes small ripples. A strong storm wind can make waves as tall as a house! When a wave reaches the shore, it curls over and crashes onto the sand.
Fill a baking pan with water and blow gently across the top. Watch the ripples form — that's the same thing wind does to the whole ocean, just much, much bigger.
The Moon Pulls the Tide
Tides are different from waves. Tides happen because the Moon's gravity gently tugs on Earth's oceans, pulling the water toward it. Most beaches get two high tides and two low tides every day, and each full cycle takes about 24 hours and 50 minutes — a little longer than one day.
High Tide, Low Tide: What Changes?
At high tide, the ocean covers more of the beach. At low tide, the water pulls back and uncovers rocky pools full of crabs, starfish, and snails. In the Bay of Fundy in Canada, the tide can rise more than 16 meters (about 53 feet) — tall enough to cover a five-story building!
Match each ocean word to what it means.
Terms
Definitions
Drag terms onto their definitions, or click a term then click a definition to match.
What mainly causes ocean waves?
About how many high tides does most of the ocean get in one day?
Build a Wave Bottle
Fill a clear plastic bottle about halfway with water and add a few drops of blue food coloring. Fill the rest with vegetable oil and screw the cap on tight (ask an adult to help seal it). Tip the bottle slowly side to side and watch a wave form where the oil and water meet. Draw a picture of your wave and label the 'crest' (top) and 'trough' (bottom).
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