Chapter 5 Clickers

ConceptualIntegrated Science

Second Edition

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Gravity

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Gravity was discovered by

a) Aristotle.

b) Galileo.

c) Isaac Newton.

d) early humans.

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Gravity was discovered by

a) Aristotle.

b) Galileo.

c) Isaac Newton.

d) early humans.

Explanation:

Early humans discovered gravity. Newton's discovery was that gravity is universal—existing everywhere.

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The concept of free-falling objects applies to

a) apples.

b) the Moon.

c) both of the above.

d) neither of the above.

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The concept of free-falling objects applies to

a) apples.

b) the Moon.

c) both of the above.

d) neither of the above.

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If the distance between two planets doubles, the force of gravity between them

a) doubles.

b) quadruples.

c) decreases by half.

d) decreases by one-quarter.

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If the distance between two planets doubles, the force of gravity between them

a) doubles.

b) quadruples.

c) decreases by half.

d) decreases by one-quarter.

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If the distance between two planets decreases to half, the force of gravity between them

a) doubles.

b) quadruples.

c) decreases by half.

d) decreases by one-quarter.

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If the distance between two planets decreases to half, the force of gravity between them

a) doubles.

b) quadruples.

c) decreases by half.

d) decreases by one-quarter.

Explanation:

Twice as close means four times the force (inverse-square law). Can you see that if the distance were instead doubled, the force would be one quarter?

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When the distance between two stars decreases by one-tenth, the force between them

a) decreases by one-tenth.

b) decreases by one-hundredth.

c) increases 10 times as much.

d) increases 100 times as much.

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When the distance between two stars decreases by one-tenth, the force between them

a) decreases by one-tenth.

b) decreases by one-hundredth.

c) increases 10 times as much.

d) increases 100 times as much.

Explanation:

This refers to the inverse-square law of gravity. Ten times closer means 100 times the force. Can you see if the distance were increased by ten the force would be 1/100?

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Consider light from a candle. If you're five times as far away, its brightness will look about

a) one-fifth as much.

b) one-tenth as much.

c) one twenty-fifth as much.

d) the same brightness at any reasonable distance.

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Consider light from a candle. If you're five times as far away, its brightness will look about

a) one-fifth as much.

b) one-tenth as much.

c) one twenty-fifth as much.

d) the same brightness at any reasonable distance.

Explanation:

Five times as far, according to the inverse-square law, is 1/25 the brightness. Likewise for the sound of a chirping cricket!

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Consider a space probe at a distance five times Earth's radius. Compared with gravitational force at Earth's surface, its gravitational attraction to Earth at this distance is about

a) one-fifth as much.

b) one-tenth as much.

c) one twenty-fifth as much.

d) the same gravitation at any reasonable distance.

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Consider a space probe at a distance five times Earth's radius. Compared with gravitational force at Earth's surface, its gravitational attraction to Earth at this distance is about

a) one-fifth as much.

b) one-tenth as much.

c) one twenty-fifth as much.

d) the same gravitation at any reasonable distance.

Explanation:

Five times as far (inverse-square law) means 1/25 the gravitational attraction.

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If the Earth's radius somehow shrunk, your weight on the shrunken surface would be

a) less.

b) more.

c) unchanged.

d) none of the above.

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If the Earth's radius somehow shrunk, your weight on the shrunken surface would be

a) less.

b) more.

c) unchanged.

d) none of the above.

Comment:

The idea of surface force increasing when a star shrinks leads to the huge forces near an ultimate shrunken star—a black hole.

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If the Sun were twice as massive, its pull on Earth would be

a) unchanged.

b) twice.

c) half.

d) four times as much.

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If the Sun were twice as massive, its pull on Earth would be

a) unchanged.

b) twice.

c) half.

d) four times as much.

Explanation:

Let the equation for gravity guide your thinking. When one mass is doubled, with all else being the same, the force doubles.

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Strictly speaking, compared with your weight on the ground, your weight at the top of a very tall ladder would be

a) less.

b) more.

c) no different, really.

d) none of the above.

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Strictly speaking, compared with your weight on the ground, your weight at the top of a very tall ladder would be

a) less.

b) more.

c) no different, really.

d) none of the above.

Explanation:

This follows from the inverse-square law, where the distances involved are the Earth's radius versus the Earth's radius plus the height of the ladder. In a ractical sense, there's no measurable difference.

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According to the equation for gravity, if you travel far enough from Earth, the gravitational influence of Earth will

a) reach zero.

b) still be there.

c) actually increase.

d) none of the above.

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According to the equation for gravity, if you travel far enough from Earth, the gravitational influence of Earth will

a) reach zero.

b) still be there.

c) actually increase.

d) none of the above.

Explanation:

Look at the gravity equation: as d approaches infinity, F approaches zero—but never reaches zero.

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You are weightless when you are

a) in free fall.

b) without a support force.

c) infinitely away from all mass.

d) all of the above.

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You are weightless when you are

a) in free fall.

b) without a support force.

c) infinitely away from all mass.

d) all of the above.

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When an astronaut in orbit is weightless, he or she is

a) beyond the pull of Earth's gravity.

b) still in the grip of Earth's gravity.

c) in the grip of interstellar gravity.

d) none of the above.

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When an astronaut in orbit is weightless, he or she is

a) beyond the pull of Earth's gravity.

b) still in the grip of Earth's gravity.

c) in the grip of interstellar gravity.

d) none of the above.

Comment:

If the astronaut were not in the grip of Earth's gravity, would his or her circling the Earth occur? Interstellar gravity plays a significantly lesser role.

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When you stand at rest on a weighing scale, the force due to gravity on you is

a) equal in magnitude to the support force of the scale.

b) almost equal to the support force of the scale.

c) actually absent.

d) none of the above.

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When you stand at rest on a weighing scale, the force due to gravity on you is

a) equal in magnitude to the support force of the scale.

b) almost equal to the support force of the scale.

c) actually absent.

d) none of the above.

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Inhabitants in the International Space Station orbiting the Earth are

a) weightless.

b) in the grip of Earth's gravity.

c) without a support force.

d) all of the above.

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Inhabitants in the International Space Station orbiting the Earth are

a) weightless.

b) in the grip of Earth's gravity.

c) without a support force.

d) all of the above.

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The center of gravity of an object is located at the

a) point of its average weight.

b) geometric center.

c) heaviest portion of the object.

d) all of the above.

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The center of gravity of an object is located at the

a) point of its average weight.

b) geometric center.

c) heaviest portion of the object.

d) all of the above.

Comment:

Can you see that the center of gravity of a baseball bat is closer to its heavier end?

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The center of gravity of your body

a) is located in your midsection.

b) varies with body position.

c) remains within your body.

d) none of the above.

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The center of gravity of your body

a) is located in your midsection.

b) varies with body position.

c) remains within your body.

d) none of the above.

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Centripetal force is any force that

a) acts on a rotating object.

b) produces circular motion.

c) pulls objects outward when they whirl about a central point.

d) takes the place of gravity.

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Centripetal force is any force that

a) acts on a rotating object.

b) produces circular motion.

c) pulls objects outward when they whirl about a central point.

d) takes the place of gravity.

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In a future rotating space habitat, centripetal force can provide

a) a steady rotational speed.

b) weightlessness.

c) a right-angle force for inhabitants.

d) a support force sensed as weight.

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In a future rotating space habitat, centripetal force can provide

a) a steady rotational speed.

b) weightlessness.

c) a right-angle force for inhabitants.

d) a support force sensed as weight.

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In the absence of air drag, a projectile follows a curved path

a) when it crosses a gravitational field.

b) due to a combination of constant horizontal motion and accelerated downward motion.

c) called a parabola.

d) all of the above.

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In the absence of air drag, a projectile follows a curved path

a) when it crosses a gravitational field.

b) due to a combination of constant horizontal motion and accelerated downward motion.

c) called a parabola.

d) all of the above.

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The speed of a bowling ball rolling along a smooth alley is

a) not affected by gravity.

b) constant.

c) both of the above.

d) none of the above.

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The speed of a bowling ball rolling along a smooth alley is

a) not affected by gravity.

b) constant.

c) both of the above.

d) none of the above.

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When no air resistance acts on a projectile, its horizontal acceleration is

a) g.

b) at right angles to g.

c) centripetal.

d) zero.

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When no air resistance acts on a projectile, its horizontal acceleration is

a) g.

b) at right angles to g.

c) centripetal.

d) zero.

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Without air resistance, the time for a vertically tossed ball to return to where it was thrown from is

a) 10 m/s for every second in the air.

b) the same as the time going upward.

c) less than the time going upward.

d) more than the time going upward.

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Without air resistance, the time for a vertically tossed ball to return to where it was thrown from is

a) 10 m/s for every second in the air.

b) the same as the time going upward.

c) less than the time going upward.

d) more than the time going upward.

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With air resistance, the time for a vertically tossed ball to return to where it was thrown from is

a) 10 m/s for every second in the air.

b) the same as the time going upward.

c) less than the time going upward.

d) more than the time going upward.

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With air resistance, the time for a vertically tossed ball to return to where it was thrown from is

a) 10 m/s for every second in the air.

b) the same as the time going upward.

c) less than the time going upward.

d) more than the time going upward.

Explanation:

Consider a feather tossed upward. It reaches its zenith rather quickly but falls back to its starting place slowly. The same is true of a ball tossed in air, though not as pronounced.

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When air resistance is negligible, the component of velocity that doesn't change for a projectile is the

a) horizontal component.

b) vertical component.

c) a combination of horizontal and vertical components.

d) none of the above.

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When air resistance is negligible, the component of velocity that doesn't change for a projectile is the

a) horizontal component.

b) vertical component.

c) a combination of horizontal and vertical components.

d) none of the above.

Explanation:

That's because there is no horizontal force. What can you say about the vertical component of velocity?

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Air resistance on a projectile

a) lessens its range.

b) lessens its height.

c) both of the above.

d) none of the above.

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Air resistance on a projectile

a) lessens its range.

b) lessens its height.

c) both of the above.

d) none of the above.

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The first person(s) to publish writings about Earth satellites was

a) Aristotle.

b) Isaac Newton.

c) Albert Einstein.

d) Hewitt, Lyons, Suchocki, and Yeh.

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The first person(s) to publish writings about Earth satellites was

a) Aristotle.

b) Isaac Newton.

c) Albert Einstein.

d) Hewitt, Lyons, Suchocki, and Yeh.

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In a circular orbit, the gravitational force on a satellite is

a) constant in magnitude.

b) at right angles to satellite motion.

c) a centripetal force.

d) all of the above.

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In a circular orbit, the gravitational force on a satellite is

a) constant in magnitude.

b) at right angles to satellite motion.

c) a centripetal force.

d) all of the above.

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A satellite in elliptical orbit about Earth travels fastest when it moves

a) close to Earth.

b) far from Earth.

c) in either direction—the same everywhere.

d) between the near and far points from Earth.

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A satellite in elliptical orbit about Earth travels fastest when it moves

a) close to Earth.

b) far from Earth.

c) in either direction—the same everywhere.

d) between the near and far points from Earth.

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A satellite in orbit around the Earth is above Earth's

a) atmosphere.

b) gravitational field.

c) both of the above.

d) neither of the above.

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A satellite in orbit around the Earth is above Earth's

a) atmosphere.

b) gravitational field.

c) both of the above.

d) neither of the above.

Explanation:

Don't say above Earth's gravitational field! If it were, it wouldn't circle Earth.