Name ______Date ______Period ______

Inquiry 15: Gravity and Orbital Motion

Part A. Watch the Starry Night demo and make some general observations about the movements of the planets around the Sun.

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Inquiry 15.1

  1. What pulling force acts on the tennis ball at all times? ______

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  1. When you rolled the tennis ball slowly, how did it move once it left the table?

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  1. How does the forward speed of the tennis ball affect the motion of the ballonce it leaves the table?

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  1. All planets that orbit the Sun are traveling forward due to inertia and falling toward the Sun due to gravity. Describe the path of something that has forward motion but is also being pulled down by gravity.

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Inquiry 15.2

  1. Describe the motion of the marble when an unbalanced force (metal ring) influences it.

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  1. Describe the motion of the marble when the unbalanced force is removed.

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  1. Planets move forward due to inertia and inward due to an unbalanced force (causing the planets’ paths to curve). What is the unbalanced force that keeps the planets in orbit? What would happen to the planets without this unbalanced force?

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Inquiry 15.3

  1. Describe how the marble moved when the mass in the center (the balloon) was NOT present.

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  1. Describe how the marble moved when the mass in the center was present.

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  1. As the distance between the balloon and the marble decreased, what happened to the marble’s speed?

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  1. Based on your observations, which planet do you think would have the fastest orbital speed? What evidence do you have to support your answer?

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  1. What force keeps the planets in their orbital paths around the Sun?

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  1. Scientists have discovered that stars “wobble” or move; they believe that a wobbling star indicates that a planet is nearby. Why might this be so?

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Inquiry 15.4

  1. What do the objects in this demonstration represent?

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  1. What would happen to the sphere if the string was cut in the middle of the demonstration?

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  1. How does the mass of the cylinder affect how fast or slow the sphere orbits your hand?

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  1. We know that Jupiter is more massive than Earth. Jupiter has a moon named Io that is similar in mass and diameter to Earth’s moon; both satellites are roughly the same distance from their planet. Orbital period is the time it takes a revolving object to orbit a central object. Which planetary satellite has a shorter orbital period, Io or the Moon? Why?

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  1. In lesson 14 you learned the approximate mass of each planet. How do you think scientists determine the mass of the planets?

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