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9.1

# 9.1. 9.2 9.3 9.4 Force due to Gravity 9.5 Gravity drops with distance

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• 9.*

• 9.*

• 9.*

• 9.*Force due to Gravity

• 9.*Gravity drops with distance

• 9.*Weight /weightlessness + effects of Acceleration

• 9.*TidesNeap TideSpring Tide

• 9.*

• 9.*

• 9.*Science Fiction

• 9.*-- Questions --MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

• 9.*1) Consider two planets in space that gravitationally attract each other. If the masses of both planets are doubled, and the distance between them is also doubled, then the force between them is one quarter. B) half as much. C) twice as much. D) four times as much. E) none of these.

2) There are no tides to be seen in the community swimming pool because A) it is shallow compared to the ocean. B) all parts of it are practically the same distance from the moon. C) gravitation on the small mass of water is negligibly small. D) they are masked by the much stronger pull of Earth gravity. E) but there are, at nightime.

• 9.*3) The force of gravity acts on all apples on an apple tree. Some apples are twice as far from the ground as others. These twice-as-high apples, for the same mass, have A) practically the same weight. B) 1/4 the weight. C) 1/2 the weight.

4) Newton discovered A) gravity. B) that gravity is universal. C) neither.

• 9.*5) When the distance between two stars decreases by half, the force between them A) stays the same. B) decreases by one-quarter. C) decreases by one-half. D) increases to twice as much. E) increases to four times as much.

6) The reason the moon does not crash into the Earth is that the A) gravitational pull of other planets keeps the moon up. B) moon has less mass than the Earth. C) Earth's gravitational field is weak at the moon. D) moon has a sufficient tangential speed. E) none of these.

• 9.*7) If the mass of the Earth somehow increased with no change in radius, your weight would stay the same. increase also. C) decrease.

8) The factor most directly responsible for making a black hole invisible is its A) size. B) surface escape velocity. C) mass. D) color. E) none of these.

• 9.*9) According to Newton, doubling the distance between two interacting objects A) multiplies by 4 the gravitational force between them. B) divides by 4 the gravitational force between them. C) divides by 2 the gravitational force between them. D) multiplies by 2 the gravitational force between them.

10) If the moon were covered with water, tidal effects by Earth would find the moon with A) 1 tidal bulge. B) 2 tidal bulges. C) 3 tidal bulges. D) 4 tidal bulges. E) no tidal bulges.

• 9.*11) Tides rise and fall A) the same distance in all parts of the world. B) greatly different distances in different places.

12) Both Newton and Kepler considered forces on the planets. Kepler hypothesized the direction of the forces was A) along their directions of travel. B) toward the sun. C) neither.

• 9.*13) A black hole is A) an empty region of space with a huge gravitational field. B) simply the remains of a giant star that has undergone gravitational collapse. C) a small region that contains the mass of many galaxies.

14) The best time for digging clams (when the low tide is extra low) is during the time of the half moon. B) new or full moon. C) quarter moon. D) ...none of these times in particular.

• 9.*15) When a star collapses to form a black hole, its mass remains the same. increases. C) decreases.

• 9.*-- Answers --MULTIPLE CHOICE. The one alternative that best completes the statement or answers the question.

• 9.*Chapter 9

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