Mod H Unit 2 Lesson 4 - Gravity in the Universe

The moon revolves around Earth. The moon travels at a speed of about 1 km/s. What keeps the moon in orbit around Earth?

• gravity

• magnetism

• ocean tides

• nuclear fusion

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Two objects have a certain gravitational fore between them. What would happen if the mass of one of the objects suddenly increased?

• The mass of the other object would increase

• The distance between the objects would increase.

• The gravitational force of the ojects would remain constant.

• The gravitational force between the two objects would increase.

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Why are Earth, other solar system planets, and most planetary objects spherical?

• force of gravity acting evenly in all directions around the center of mass

• erosion made by asteroids hitting the object's surface at the time of formation

• heat received from the sun melting the objecct's surface at the time of formation

• pressure of atmosphere acting evenly in all directions on the object's surface

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Planets are held in their orbit because of their large sizes as well as a certain force that acts over a distance. Which force is responsible for acting on the planets?

• nuclear force

• electrical force

• magnetic force

• gravitational force

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Here is a model of the gravitational force of Mars. Objects A and B have the same mass but are different distances from Mars. Which statement explains how the gravitational force affects the two objects?

• Object A and B will be affected equally by the gravitational force.

• Object B will be more affected by the gravitational force because it is closer to Mars than Object A.

• Object A will be more affected by the gravitational force because it is farther from Mars than Object B.

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The satellite is orbiting Earth in the direction shown and is pulled toward Earth by gravity. What would happen if Earth's gravity suddenly disappeared?

• The satellite would fall to Earth.

• The satellite would stop moving.

• The satellite would continue to orbit Earth.

• The satellite would move into space in a straight line.

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The dotted lines in the picture show orbital paths of objects. Which statement is true about all of the orbits shown?

• All objects move in circular orbits.

• The size of an object determines the size of its orbit.

• The force of gravity is what holds each object in its orbit.

• The size of both an object and the object it orbits are equal.

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Observe the path of Voyager 2 satellite . Why did the route of Voyager 2 change, without firing its thrusters, as it passed Jupiter?

• Gravitational force between Jupiter and Voyager 2 pulled it into a new route.

• Solar winds pushed Voyager 2 into a new path.

• Jupiter blocked the sun’s gravitational pull on Voyager 2.

• The gravity of Jupiter caused Voyager 2 to become its satellite.

Answer explanation

Large planets have enough mass to exert a significant pull on an object traveling near them. Scientists used the gravitational forces of the large planets to give Voyager a “boost” so that it moved faster.

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Which of the following did engineers need to know to plan Voyager 2’s path through the solar system? Choose *ALL* that apply.

• the positions of the planets

• the masses of the planets

• the mass of Voyager 2

• Newton's laws of motion and the law of universal gravitation

Answer explanation

Designers needed to know the masses of all the planets, the mass of the spacecraft, and where the planets would be as Voyager 2 traveled. Additional knowledge of Newton’s laws of motion and the law of universal gravitation were needed to predict how the masses of planets would affect the satellite’s motion.

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The chihuahua is in an elevator. What is the elevator doing at 22 seconds?

• It is moving up at a constant velocity.

• It is moving down at a constant velocity.

• It is accelerating upward.

• It is accelerating downward.

Answer explanation

The force of the elevator floor pushing up on the chihuahua is less than the force of gravity that pulls the chihuahua down. Since the force is unbalanced in the downward direction, the elevator must be accelerating downward.

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