Objective: Describe the forces that keep objects in orbit in the Solar System.
The Pull of the Planets
(an activity from the Lunar and Planetary Institute)
Purpose
Using flexible surfaces, students will model the gravitational fields of planets.
Vocabulary
 Gravitational Force – The pull that gravity has on an object.
 Gravity – The force that attracts one object to another.
Materials
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20" by 12" embroidery hoop
Something to support the edges of the embroidery hoop
Thin stretchable plastic sheet (plastic garbage bag, plastic-wrap)
4 (1/2"–wide) small marbles
1 (2") Styrofoam™ ball
Half a can of Play-Doh®
Pencil
Procedure
1. Place your embroidery hoop on the supports.
2. Place a marble on the plastic sheet. Record your observations.
3. Place a second marble on the plastic sheet. Record your observations.
4. Experiment by placing and dropping the marbles (together and separately) onto the sheet. Record your
observations.
5. Add a large, 2" round ball of Play-Doh® (represents a large "planet" alone on the sheet). Record your
observations.
6. Write a hypothesis explaining what you think will happen if the marbles are dropped onto the sheet (while
the Play-Doh® ball is on the sheet).
7. Drop your marbles and record your observations.
8. Place a very small round ball of Play-Doh® (about half of the size of a marble), which represents a small
asteroid, alone on the sheet. Record your observations.
9. Add marbles to the sheet. Record your observations.
10. Place the Styrofoam® ball alone on the sheet. Record your observations.
Objective: Describe the forces that keep objects in orbit in the Solar System.
11. Experiment with dropping the marbles in different locations, and with different amounts of Play-Doh® or
the Styrofoam® ball, in various locations on their gravity field.
Group Members ___________________________________________________________
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Absent _________________________________________________________________
The Pull of the Planets
(an activity from the Lunar and Planetary Institute)
1. Describe what happens when you place a marble on the plastic sheet.
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2. Describe what happens when you place a second marble on the plastic sheet.
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3. Describe what happens when you place and drop the marbles (together and separately) onto
the plastic sheet.
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a. Explain how this activity demonstrates gravity.
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4. Describe what happens when you place the 2” ball of Play-Doh® on the plastic sheet.
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Objective: Describe the forces that keep objects in orbit in the Solar System.
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5. Write a hypothesis explaining what you think will happen if the marbles are dropped onto
the sheet (while the Play-Doh® ball is on the sheet).
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6. Record what happened when you dropped the marbles on the plastic sheet with the PlayDoh® ball on it.
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a. Was your hypothesis (#5) correct or incorrect? Explain why or why not.
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7. Place a very small round ball of Play-Doh® (about half of the size of a marble), which
represents a small asteroid, alone on the sheet. Record your observations.
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8. Describe what happens when you add marbles to the sheet with the small ball of Play-Doh®.
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9. Describe what happens when you place the Styrofoam® ball alone on the sheet. Record your
observations.
Objective: Describe the forces that keep objects in orbit in the Solar System.
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10. What happens when drop marbles on the plastic sheet with the Styrofoam® ball?
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11. When does the Play-Doh® represent strong gravity? Weak gravity?
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12. What happens to the marbles with the strong gravity? Weak gravity?
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