How to Teach What Causes the Earth’s Tides

May 5, 2021

4 min read

Science is the systematic study of our physical and natural world. In school, students learn science as both the process of learning about the world and the information gathered from previous scientific discoveries. The topic of science is so massive that students can struggle to understand science as a method for learning about the world around them and instead focus on the individual facts collected by scientists. We can use teaching students about what causes the Earth’s tides as an opportunity to show them the interconnectedness of science.

As a teacher, you can help your students embrace science as a tool for understanding the world by how you introduce the material. Historically, teachers have taught by sharing information about the world in individual units full of facts for students to remember.

Start by Asking a Question

To reinforce what science is, next time you are teaching a topic, try this: Start with a question scientists had about the topic you are teaching. For example, if you are teaching students about tides, you may show your students a time-lapsed video of a tide rising and falling, like this one:

You will want to define a tide to make sure that every student in your class knows what a tide is.

Then, ask your students why they think the water rises and falls. Most likely, they won’t know the answer, but thinking about it will show them how scientists make discoveries.

Learning About What Causes the Earth’s Tides

Next, tell your students the story of how real scientists figured out what caused the tides. I like to include when scientists got it wrong in addition to when they were right because it reinforces that science is a living practice. People make guesses based on what they know at the time. When more information is known, better guesses are made.

The story of the tides goes all the way back to Alexander the Great, or even farther. Alexander the Great’s soldiers first saw the tides when they reached the Indian Ocean. They believed the gods protected the land from invasion using the tides.

In the early 1600s, Kepler, a German astronomer, believed the Earth was a living creature, and the tides were caused by it breathing in and out twice a day. Others thought ocean water traveling in and out of a hole in the Earth created the tides.

By the mid-1600s, Descartes, a French philosopher, suggested that the tides were related to the Moon.

Then, in 1687, using his new theory of gravity, Isaac Newton explained that the tides were caused by water being pulled by gravity from both the Moon and the Sun.

Now that students understand how the information was discovered, they are ready to spend time getting to know Newton’s explanation of the tides. I like to use a variety of resources so that students can choose how they learn best. I especially like including videos because I think they make it easier for students to understand concepts they don’t see in their everyday lives.

Here are a few videos on tides I would use:

Of course, I also have a reading passage all about the tides. You can help your students learn what causes the Earth’s tides with the reading passage. Click the picture to get the tides reading passage at Teachers Pay Teachers.

Everything in Science is Connected

Once students understand tides, I can stretch their learning by connecting it to new topics. Students will be ready to learn about tide pools, weathering and erosion at beaches and cliffs along the ocean, and the fact that the Earth’s rotation is slowing.

Yep, the Earth’s rotation is slowing because of the tides on Earth. As the Earth spins, it pushes the water in the oceans slightly ahead of the Moon’s pull. In response, the Moon pulls back on the water. This backward pull from the Moon slows the rotation of the Earth. Every year, one day on the Earth gets about 1.4 milliseconds longer.

Eventually, the Earth’s rotation will slow so much that, like the Moon faces the Earth, one side will always face the Sun. This process is called a tidal lock. Stephen Dole first explained tidal lock in his book, Habitable Planets for Man, in the early 1960s.

The leading tides also transfer energy to the Moon and push it farther away from the Earth. Each year, the Moon gets about four centimeters farther away from Earth. Eventually, after hundreds of millions of years, the Moon will take about 47 days to orbit the Earth. However, the Moon will never entirely leave the Earth because by the time it would be pushed too far away from the planet, the Sun will have transformed into a red dwarf, no longer able to sustain the solar system as we know it.

Now, we are talking about red dwarfs and how stars work. See? Everything in science is connected. We want to show our students these connections as we teach them how to make discoveries about the world based on the work of scientists who have come before us.

Focus on the Story of a Scientific Discovery

When you are making your lesson plans, think about ways you can tell the story of how a discovery was made, how the topic connects to what your students already know, and what your students don’t know about yet but will learn.

I love using stories to teach science. My History of Chemistry reading passage set shows how the science of chemistry evolved from the first alchemists to the discovery of the strong nuclear force. You can get the reading passages individually or get the entire set for a discount: