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Ocean Tides Lesson for Kids

Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

Ocean water goes up and down each day, and we call these tides. In this lesson we will learn why we have ocean tides and how they happen. We will also learn about two forces called gravity and inertia.

What Are Ocean Tides?

If you live near (or have visited) the ocean, you might know that the water level changes throughout the day. You can be swimming at the beach and watch the water slowly creep farther up the sand. A few hours later, the water level will go down again. This repeats on a regular cycle, every single day, and we refer to this water movement as ocean tides.

High tide is when the water level is highest, and low tide is when the water level is lowest. There are two periods of high tide and two periods of low tide every day. All together, this is called the tidal cycle.

What Causes Ocean Tides?

Ocean tides are mainly caused by the gravitational pull of the moon. Really big objects like planets and moons have their own gravitational pull, and the force of gravity gets stronger when two objects are closer to each other.

Without the gravity of the moon, the water of the ocean would be equally distributed around Earth.
Ocean water without gravity

The moon is the closest planet-like object to Earth. In fact, Earth's gravitational pull keeps the moon in orbit around the Earth. But, because the Earth and moon are so close to each other, the moon also exerts a gravitational force on the Earth, and we see this in the ocean tides.

This picture shows you how the moon affects the oceans on Earth.

The moon influences the ocean tides.
Ocean tides

Earth spins (or rotates) one full turn every day. At the same time, the moon is orbiting around Earth. Because both objects are moving, the moon changes its position relative to Earth throughout the day and night.

There are two high tides occurring at the same time. One high tide occurs where the moon is closest to Earth, and the water gets pulled toward the moon until land stops it. This high tide is caused by gravity and causes water to accumulate near the shoreline.

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