Using Gravity to Learn About Space

Navigate the knowledge tree: 🌿 Earth & Space Science ➡ Astronomy ➡ Ways of Understanding and Exploring

Learning Intentions

By the end of this topic, you should be able to:

State what gravity is and how it works in space.
Explain how astronomers can figure out the mass of a planet.

Glossary

Key terms and definitions.

gravity: The force that pulls things towards each other.

mass: The amount of matter in an object.

orbit: The path one object takes as it moves around another object in space.

revolution: The movement of one object around another, like Earth orbiting the Sun.

speed: How fast something is moving; distance travelled in a given amount of time.

How Gravity Works in Space

Anything that is made of materials has mass, and anything that has mass also has gravity. The more mass something has, the more gravity it has.

Gravity causes objects in space to be pulled towards each other, but gets weaker as the objects get farther apart from each other.

Activity: Gravity Storyline and Simulator

Go to this website: https://www.testtubegames.com/weightless.html

Click on "Find Out"
Make your way through the simulation by:
- - Clicking on the text to confirm each step
  - Clicking and dragging the interactive parts
  - Eventually flying your own rocket!

How Gravity Makes Things Orbit in Space

The gravity of the object affects other objects nearby in space. Gravity pulls objects in space together (red arrows). If the light object happens to be moving at the right speed sideways (blue arrows), it can revolve around a heavier object without being pulled in.

For example, a planet's gravity affects the way moons move around a large planet. The moon's movement is exactly the right speed to stay in orbit for the Earth's gravity.

Astronomers study the way these moons move around and can use calculations to figure out how much the planet's gravity is affecting the moon. By watching moons go around planets and timing how long it takes to revolve around the planet, astronomers can figure out how strong the planet's gravity must be. This allows us to figure out the mass of the planet.

Activity: Gravity In Space Simulation

Please go to this website: https://lab.nationalmedals.org/gravity.php

Click and hold the object changing its mass.
Click, drag and quickly release the object to make it move.

Part 1: Put two small objects side-by-side in space.

What happens when you allow them to move on their own?

Part 2: Put a small and large object side-by-side in space.

What happens when you allow them to move on their own?
Which object moved the most?
Why do you think that is?

Part 3: Make a small object revolve around a larger object.

What did you need to do to the small object to make it move in a circle?
Why do you think the larger object cannot revolve around the smaller one?

Part 4: Try to get multiple small objects revolving around a large one, like moons around a large planet.

What did you need to do so that they would all stay in their orbits, and not fly off into space or crash into other objects?

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