Lesson 3.3
Name
Date
Period ____________
Chapter 3: Lesson 3- Gravity and Motion
What Keeps Objects in Orbit?
1. IDENTIFY: What two factors keep a planet in orbit around the sun?
2. DRAW CONCLUSIONS: What keeps Earth from falling into the sun?
3.
How would a planet move if the sun suddenly disappeared? Explain.
How Does Gravity Help Form Planets, Stars, and Solar Systems?
4. IDENTIFY: What is accretion?
5. DRAW CONCLUSIONS: What would happen to a solar system if gravity suddenly stopped working?
Building Vocabulary: Write a definition for each of these terms.
5. orbit:
__________________________________________________________________________________
6. force: _________________________________________________________________________ ____
7. gravity: ________________________________________________________________________ ____
8. law of universal gravitation: ____________________________________________________________
__________________________________________________________________________________
9. mass: _________________________________________________________________________ ____
10. weight: ____________________________________________________________________________
11. inertia: ________________________________________________________________________ ____
12. Newton’s first law of motion: ___________________________________________________________
__________________________________________________________________________________
13. accretion: ______________________________________________________________________ ____
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Lesson 3.3
14. Explain what determines the force of gravity between two objects and what keeps Earth and the moon
in orbit.
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Lesson 3.3
Understanding Main Ideas: Answer the following questions in the spaces provided.
15. How are gravity and weight related?
16. How does Newton’s law of universal gravitation apply to Earth and the moon?
17. How does distance affect the strength of the force of gravity?
18. How do scientists believe solar systems begin?
If the statement is true, write true. If the statement is false, change the underlined word
or words to make the statement true.
19. _____________ Newton’s first law of inertia says that an object at rest will stay at rest and an object in
motion will stay in motion unless acted on by a force.
20. _____________ Inertia and distance combine to keep Earth in orbit around the sun and the moon in
orbit around Earth.
21. _____________ Newton’s law of planetary gravitation states that every object in the universe attracts
every other object.
22. _____________ Gravity plays an important role in forming solar systems, stars, and planets.
23. _____________ Earth’s gravity pulls the moon outward.
Fill in the blank to complete each statement.
24. The amount of matter in an object is its _____________.
25. _____________ attracts all objects toward each other.
26. An object with greater _____________ is more difficult to stop or start.
27. The _____________ of two objects and their distance from each other determine the gravitational force
between them.
28. The measure of the force of gravity on an object is the object’s _____________.
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Lesson 3.3
Read the passage and complete the table below. Then answer the questions that follow.
Your Weight in the Solar System
Each object in the solar system has a different mass and diameter. As a result, you would have a
different weight on the moon than on Mars or on earth. Use the table below to calculate a person’s
weight on the surfaces of some solar system objects. In the case of the sun, you’ll have to use your
imagination. It’s really impossible to stand on the sun’s gaseous surface. For your calculations, use the
example of an astronaut who weighs 150 pounds on earth. In your calculations, use newtons instead of
pounds. One pound is about equal to 4.5 newtons.
To find your weight on the surface of each object, multiply your weight on earth by the proportion of
earth’s gravity for each object. Enter your weight on each object into the table.
Solar System Object
Proportion of
Weight on Surface
Earth’s Gravity
Moon
0.165
Venus
0.905
Mars
0.379
Pluto
0.059
Sun
274
29. Which object has a much higher gravitational attraction than Earth? Explain.
30. On which object would you weigh the least? Why do you think this is so?
31. Could you jump higher on Venus or on Mars?
32. During the Apollo program, astronauts played golf on the moon. How do you think the moon’s low
gravity affected their game?
33. Imagine that the sun contracted to a smaller volume. How would this affect the gravitational force
on its surface?
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