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Teach Gravity & Orbits
with Universe Sandbox ²

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Gravity & Orbits

Today we will take a look at orbits and gravity. How do they really work? What affects orbits?

Teacher Resources

This lesson takes a closer look at fundamental concepts of astronomy, including gravity, Newton’s three laws of motion and orbits. First, this lesson features a theory background for these concepts, followed by tasks the students complete in the simulator. These tasks are related to these concepts and help to visualize them in a compelling way.

  • Theory: This lesson takes a closer look at the effects of gravity and continues the theme of orbits.
  • Play: The students complete various tasks in the game that explore the effects of gravity.
  • Share & Discuss: These topics focus on gravity and orbital mechanics.


  • Gravity is a force of attraction that exists between any two masses, any two bodies, any two particles.
  • The greater the mass of anything, the greater its gravity. We do not know what gravity "is" in any fundamental way - we only know how it behaves (source).
  • g: the acceleration due to gravity on everyday objects near the Earth's surface. Symbol: g (SI unit).

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Teacher Resources

Newton's Three Laws of Motion

First Law
Objects at rest remain at rest and objects in motion remain in motion in a straight line unless acted upon by an unbalanced force.

Second Law
Force equals mass times acceleration (or f = ma).

Third Law
For every action there is a an equal and opposite reaction.

Teacher Resources


  • The curved path, usually elliptical, described by a planet, satellite, spaceship, etc., around a celestial body, as the Sun. (source)
  • The result of a perfect balance between the forward motion of a body in space, such as a planet or moon, and the pull of gravity on it from another body in space, such as a large planet or star. (source)

Planet Nine Orbit.

Teacher Resources


Lesson Goal

Load our solar system. Write down the velocity of three or more planets. What do you notice?

Show Notes

Clicking on a planet and then looking at the motion tab allows you to see the velocity of the planet. If you compare the velocities of different planets, it’s clear that planetary bodies closer to the Sun move faster. They do so so that they can maintain orbit: if they moved slower, they would crash into the Sun.

Load up Earth & Moon. Add several soccer balls to orbit Earth. Pause the simulation and try making the balls faster and slower. What happens in these two cases?

Show Notes

Both speeding up and slowing down the soccer ball changes its orbit. If the ball is sped up enough it moves so fast it liberates itself from Earth's gravity, and if it is slowed down enough it will crash into the Earth. All this means is that orbit is actually just falling while moving sideways so fast you never hit the ground. Orbiting is actually just falling.

Experiment with adding black holes to our solar system. What happens?

Show Notes

If some students are ready early on, it’s a good idea to let them experiment. Some concepts they can try out: black holes, supernovas, dwarf planets, creating their own universes.

How to Play

As you launch the game, you can immediately start playing with the Solar System.

Gameplay screenshot

To access other simulations at any time, press Esc. Then, select Open to load any of the simulations included in the game.

Gameplay screenshot

After you've clicked Open, click on any of the simulations to load them.

Gameplay screenshot

Share & Discuss

Share & Discuss

Orbital movement is caused by gravity. True or false? How do orbits work?

Show Notes

Orbital movement is caused by gravity. A celestial body in orbit is effectively falling towards something, but moving at such a speed that it orbits the other body rather than crashing into it. An orbit is a careful balance with the gravity and velocity of the two celestial objects. With large objects, such as the Sun, the gravity is so significant that multiple objects can orbit the entity far away from each other.

How does distance affect gravity?

Show Notes

Distance dramatically reduces the effects of gravity (although gravity technically has an infinite range). The effect of gravity between two objects is inversely proportional to the square of the distance between the two objects.

What would happen if the Sun exploded in terms of celestial movement?

Show Notes

This can be tested out in the Simulator by selecting the “explode” tool (under the “power” tab) and clicking on the Sun. Since the Sun would simultaneously no longer provide a gravitational pull and the explosion would be potent, everything in the solar system would be pushed away from the center of the explosion. If you have time, it’s a good idea to show how this would play out in the simulator on the screen so the students can see the phenomenon in real time.

BONUS QUESTION: What would happen to the orbits of the planets if the Sun turned into a black hole with the same mass?

Show Notes