Objective I Can Demonstrate Forces That Keep Objects in Orbit in the Solar System

Objective – I can demonstrate forces that keep objects in orbit in the Solar System.

Names ______

______

Absent ______

Staying Up While Falling Down

This activity demonstrates how a satellite (natural or man-made) stays in orbit by modeling the effects of Earth’s gravity on a satellite and the Sun’s gravity on the planets. Participants will observe gravity acting as a centripetal “center-seeking” force.

Question

·  How does the amount of gravitational force affect a planet orbiting the Sun?

Materials

Ê Plastic golf ball

Ê String

Ê PVC pipe

Ê Different size washers

1. Thread the string through the straw. DO NOT tie a washer to the other end of the string. Your set up should look like the diagram below (except no washer).

I. Gather (Record your observations describing what happens with as you add weight to your string [representing amount of gravitational force pulling on your planet].)

Hold the straw and swing the ball (no washer attached) in a circle so that it “orbits” the straw. (Be sure to keep moving your hand at a constant speed.) Record your observations.

Tie a small washer to the end of the string. Hold the straw and swing the ball in a circle so that it “orbits” the straw. (Be sure to keep moving your hand at a constant speed.) Record your observations.

Tie a medium sized washer to the end of the string. Hold the straw and swing the ball in a circle so that it “orbits” the straw. (Be sure to keep moving your hand at a constant speed.) Record your observations.

Tie a large washer to the end of the string. Hold the straw and swing the ball in a circle so that it “orbits” the straw. (Be sure to keep moving your hand at a constant speed.) Record your observations.

Tie two or more large washers the end of the string. Hold the straw and swing the ball in a circle so that it “orbits” the straw. (Be sure to keep moving your hand at a constant speed.)

II. Reasoning (Analysis/Analyze/What does the data I gathered in Step I telling our group?) (Be sure to include an analysis of what happens as you increase weight on the golf ball “planet.”)

III. Communication (Come to a conclusion and use your evidence from Part II to support your conclusion. Remember, you are answering the question – How does the amount of gravitational force [as represented by the washer(s)] affect a planet orbiting the Sun?)

We have your rovers. If you want them back, send 20 billion Martian bucks. No funny business or you will never see them again.

- Seen on a hall wall at NASA's Jet Propulsion Lab

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