Hi, I'm Trish, Programs Coordinator at the Space Centre.
Understanding how tides work are one of those things that can really be a workout for your brain. We all know that there are high tides and low tides, but do you know that they are all caused by the Moon, Sun, and Earth, and this thing called gravity?
When I talk to kids about gravity, I compare it to a superpower even more powerful that Superman. (If you would like a refresher on gravity have a look at our activities here. Superman can’t move the water in the ocean, but gravity can. Although gravity is the super force at work it is really the Moon who is the superhero in the story about tides. The Moon’s influence, or gravitational pull, is what causes the tides. So are you ready for your brain workout?
This is how tides work:
Imagine a ball with a thin skin of water over its surface – this is Earth. Now picture the Moon orbiting Earth. The Moon’s gravitational pull results in a bulge of water on the side it is closest to and the side farthest away. This is high tide.
In British Columbia we have two high tides and two low tides in a 24 hour and 52 minute period. The two high tides in a day are not equal – there is a ‘high’ high tide and a ‘low’ hide tide, as well as a ‘low’ low tide and a ‘high’ low tide. Have a look at this page from the local tide chart to see how tides vary over time.
This might sound simple enough but let’s dive into the ideas.
If we come back to our superhero analogy, superheroes are stronger when they work together but superheroes don’t always work together. It is the same with the Moon and Sun when we think of tides. We’ve identified the Moon as the main superhero in this story, but sometimes she has help from the Sun. The Sun’s gravitational pull also influences the tides. The Sun is far larger than the Moon (the Sun’s mass is about 27 million times that of the Moon) so now you might be wondering why the Sun isn’t the main superhero in this story. Mass isn’t the only element to consider with gravitational attraction—the distance between the two objects is also a factor. Because the Moon is much closer to Earth it has a greater effect on tides than the Sun even though the Moon is so much smaller, about twice the effect of the Sun. Even with its great distance from the Earth (149,598,000 km) the enormous mass of the Sun does affect the tides. When the Moon and the Sun work together the tides the high tides are higher, and the low tides are lower (more extreme). These are called spring tides, which is a confusing name as it doesn’t have anything to do with the season, spring. When the Sun and Moon are not aligned, their powers cancel each other out and the tides are less extreme. These are called neap tides.
Tides are something that may affect your daily life, especially if you live on the coast, but they certainly affect a whole ecosystem of animals in what is known as the intertidal zone—the area between high and low tide. The intertidal zone is a great place to explore. There are fascinating plants and animals that are adapted to living in this extreme environment. On the next low tide consider explore the intertidal zone but remember to follow a few simple rules to protect the critters that live there.
Tides aren’t just something that are experience on Earth, they are also experienced on other worlds. On these other worlds the story of tides becomes even more interesting. But I’ll leave you to do your own investigations into tides on other worlds.
Hopefully as you are reading this you’ve got some questions about some of the ideas. We’ve organised this week’s playlists to address some of the common questions about tides and the role of our superheroes, Moon, Sun and Gravity.
The Moon’s gravitational pull results in a bulge of water on the side it is closest to and the side farthest away. Watch physicist Brian Cox explain the forces at work.
Ask yourself: Why are there high tide bulges on both sides of Earth, not just on one?
See if you can replicate the movement of the Earth and the Moon to show how the two bulges form. Watch this short video and then gather up some family members and do the dance of the tides.
Ask yourself: If Earth had two moons what might happen to the pattern of the tides?
Do this activity to recreate the phases of the Moon with Oreo cookies. After you’ve completed the phases, think about how the phases affect the tides.
Build this model to help understand how tides work.
Ask yourself: What surprises you about how the tides change over the course of a day? Over a month?
Tides don’t just happen on Earth. They happen on other worlds too. Read this short article about high tide on Jupiter’s moon Io.
Ask yourself: What do you think it would it be like to live on Io with its ‘solid ground’ tides?
The Moon’s gravitational pull results in a bulge of water on the side it is closest to and the side farthest away. Read this article to find out more.
Ask yourself: Why are their high tide bulges on both sides of Earth, not just on one?
Build a model that illustrates why there is a tidal bulge on the opposite side of the Moon.
Ask yourself: How would a planetary system like Jupiter with its many moons affect the tidal bulges?
If you want a deeper explanation of tides watch this video that describes the physics behind the tidal bulges.
Ask yourself: What are some of the other concepts related to tides that you find confusing?
Read this article about the Apollo 11 experiment that helps us track changes in the Moon’s distance from Earth.
Ask yourself: How will this affect the tides on Earth?
Travel back in time with this article predicting tidal heating on Io.
Ask yourself: What are some of the ways tidal heating might affect the potential for life on other worlds?