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Spacetime is the very fabric of our universe. The bending of spacetime causes planets to orbit stars and causes black holes to form. Learn what spacetime is, then model the bending of spacetime with a planet orbiting around a star. 

Video Courtesy World Science Festival. Link 

Planet Orbit Model

See how gravity bends spacetime in this fun game.

  • Plastic Wrap

  • Circular Casserole Dish, Pot, or Similar Object

  • Tape

  • Scissor

  • Orange (Or Object with Similar Weight and Shape)

  • Marble or Similar

  • Printable Cutout Sheet for this Activity (Found at the Bottom of Cosmoto's "Week 5" Site Page)

Step 1

Cut out the circle cutout from the printable cutout sheet for this activity. Place the circle cutout inside the dish (or similar) and adjust it, if necessary, to ensure the cutout is centered inside.

Step 2

Wrap plastic wrap completely over the top of the dish and secure it to the dish using tape if necessary. The plastic wrap should be firmly on the top, but slightly loose. 

Step 3

Place the orange (or similar) on top of the clear plastic wrap that covers your dish.  The orange  should be placed over the center of the cutout as pictured below.  The orange should be lightly pressed in so as to slightly bend the plastic wrap.

After placing the orange on top, place the marble (or similar) on top of the plastic wrap that covers the dish.

How to Play

To play the game, roll the marble around the orange. The marble represents a planet and the orange represents the sun. See how many times you can get the planet to roll around the sun. 

Challenge: Get the planet to orbit around the sun 2 times.

Bonus Challenge: Get the planet to orbit around the sun 3 times.

What Does this Model Represent?

In this model, the orange represents the sun and the marble represents a planet. When you place the planet near the sun, what happens? The planet will collide with the orange. 


Space and time are linked. Together, space and time are called spacetime. The plastic wrap represents spacetime. When an object with enough mass (like the sun) bends spacetime, other objects, like planets, will move towards the sun. This is exactly what happens in our model. The orange bends the plastic wrap, which causes the marble to move towards the orange. This is how the force of gravity works: it pulls objects together through the bending of spacetime.

Orbits are formed when a planet is moving outwards into space, but the force of gravity (from the sun) pulls the planet towards the sun. Because the planet is always trying to move outwards into space and the sun is constantly pulling the planet inwards, the planet starts to orbit the sun. This is represented in our model: the marble wants to roll off the dish, but the orange's gravity is pulling the marble inward. This causes the marble to "orbit" around the orange.


Animation Courtesy NASA

Image Courtesy NASA

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