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Activity 10: Earth Formation

SPHERE OF FRIENDS

Summary:

Students become planets during this activity! Students will pretend to be particles of various masses, each having their own gravity floating around in space. Each 'particle' is drawn towards other 'particles', eventually forming a planet.

Instructional Method:

Game

Goal:

To present the importance of gravity in creating our planet and its various layers.

Objectives:

Students will be able to:

  • List the different Earth layers
  • Describe how gravity helped to produce our planet
  • Explain the differences between each of the Earth layers
  • Explain the importance of gravity in planet formation

Time:

Set up: 20 min.
Activity and discussion: 1 1/2 hr.
Clean up: 15 min.

Materials Needed:

  • Beach ball inflated and tied on a string
  • Color coded cards with respective numbers:
    Black = 6,
    Red = 5,
    Yellow = 3,
    Brown = 1,
    Blue = ½

(Enough for each student to have one, based on ratios found in the Instructional Procedures)

Vocabulary:

gravity
mass

Background:

Scientists believe that planet formation is based almost entirely on gravity. Referring to the Big Bang (an extraordinary explosion that scientists theorize is the origin of the universe), there were countless particles, or pieces of "stuff," just floating about randomly in space. As heavy or large particles attracted to each other, their gravitational pull increased, and more and more particles began to pull other particles to them. Heavier particles, with a greater mass and therefore greater individual gravity, began to form a gravitational field. As these particles bumped into one another, they began to stay together and form larger and larger groups of particles. The larger the group became, the more mass it had, and the stronger pull the group had. Eventually, it was strong enough to act on the lightest particles (now our atmosphere) and draw them into the spherical object that became the planet we call Earth.

Scientists believe that this explains how all of the planets, and possibly the stars, got their start this way. Planets are shaped in a sphere because it is the most efficient way gravity can act on other particles. Gravity originates at the center of an object and pulls other particles towards it. These particles are pulled in towards the center until they run into and are stopped by other particles that were pulled in first. Particles attract around the surface trying to get as close as they can to the center of gravity. They usually come to rest in a hole or other depression, until this depression is filled. The result of all these particles fighting to get to the center of the gravitational field without any other outside influence results in a sphere.

Instructional Procedures:

  1. Move classroom furniture to the edge of the room and attach a string to the ceiling so that the ball hangs freely approximately 3 feet (1 meter) from the ground. (This activity could also be done outside by hanging a ball from playground equipment.) This is the particle that has the most density and the most pull in the area and will attract other particles to it.
  2. Give each student a card; the colors should be randomly dispersed. Have the kids randomly place themselves in a wide area surrounding the ball. Explain that each of them have their own gravity. Students with Black cards have the most mass and therefore the most gravity. Red cards have the next largest mass, then Yellow cards, then Brown cards. Finally, Blue cards have the least amount of mass and the least amount of pull.

    - 10 kids: 1 black, 2 red, 3 yellow, 3 brown, and 1 blue
    - 15 kids: 2 black, 3 red, 4 yellow, 4 brown, and 2 blue
    - 20 kids: 2 black, 3 red, 5 yellow, 6 brown, and 4 blue
    - 25 kids: 3 black, 5 red, 7 yellow, 8 brown, and 3 blue

  3. The ball has more mass and has the highest density than any of the kids, and the kids are all being pulled slowly towards it, as well as towards each other. Have the students move the number of steps on their card towards the ball, and then stop. If they bump into other students along the way, these particles will join together and make a larger particle by adding the numbers on the cards together, (a yellow card = 3 and a brown card = 1, together they move 4 steps.) Steps should be heel to toe, to allow the game to progress evenly. The gravity of the ball is so strong that every particle wants to put one hand on the ball. If they cannot reach, have them put one hand on the shoulder of a student who has one hand on the ball. Once you are attached to the ball, STOP. More massive particles should move faster towards the object and for the most part make up the center portion of the planet. The blue particles should get to the planet last and make up the outer ring.
  4. Once all the students are attached to the planet, they want to get as close to the center of the planet as possible. If all of the shoulders of the people touching the ball are full, have the next layer of students put a hand on the shoulder of the next ring of students, who have their hands on the students who have their hands on the ball, etc. There should not be a string of five particles on one side of the ball and only two on the other. It should be equal because the gravity of the ball is pulling equally on all of the particles.
  5. Have all of the students look around and determine what the shape their planet has become (a round disc).
  6. From time to time, especially with large groups, pull out an occasional student or a few students to observe what is happening. Have them stand on a chair to see above the other students and view what is happening.

Another option is to have another set of color cards with each student's name and the color they are in the activity. Place the student's named card on the chalk board in approximately the same position they are to the ball and the other students. As the students move towards the ball have them stop every few feet and look at the board. Reposition the cards to match the students position and have the class answer questions about their positions and speed of movement; or ask them to draw it up on the board.

If you have access to a video camera, tape the exercise and watch it later with the students to see what was actually happening. Try to film it from above or higher than the student's position.

Discussion:

Why did we end up forming what is most like a circle? If we did this in space and could float in from the top or the bottom of the ball, what shape would we be (a sphere)? Why are we not in a sphere now? (The Earth's gravity forces us to stay on the ground, we can't float in from the top.) Scientists think that planets form the same way we just formed our planet. Particles are pulled together, without other gravity acting on them, and they form a spherical shape. Is the Earth spherical? Are the oceans evenly dispersed across the planet? Are they flat? What about the land? Why not? (Discuss mountains, volcanoes, etc.) If gravity is always acting on these high places trying to pull them down, why don't they just fall down? (Sometimes they do, it depends on the strength of the rock and the erosional forces that are present to determine how long it takes for these rocks to fall).

Variation:

Use a hula hoop on the ground instead of a ball, and have students sit down as they reach the center of gravity placing one hand inside the hula hoop, then one the students shoulders, etc.

For very large groups, pull a couple of people out of the game to become observers. You can make smaller color coded cards to match each student with a card, and have the observing students map the progress of each particle on the board. This might allow students within the group to see what is actually going on. These students can trade in and out of the game, particles become observers, and observers become particles.

Included National Parks and other sites:

Grand Canyon National Park

Photos:

Earth
Earth Layers

Utah Science Core:

3rd Grade Standard 3 Objective 1, 2
3rd Grade Standard 4 Objective 1, 2
6th Grade Standard 3 Objective 3

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