Chapter 9- Gravity

2) consider an apple at the top of a tree that is pulled by earth's gravity with a force of 1 N. If the tree were twice as tall, would the force of gravity be only 1/4 as strong? defend your answer.

No, because an apple at the top of the twice-as-tall apple tree is not twice as far from earth's center. the taller tree would need a height equal to the radius of the earth (6,370 km) for the apple's weight at its top to reduce to 1/4 N. Before, its weight decreases by 1% , an apple or any object must be raised 32km-nearly four times the height of Mt. Everest. So, as a practical matter, we disregard the effects of everyday changes in elevation.

Newton tested his hypothesis of gravity by comparing the fall of an apple with the fall of the moon "The moon falls ____ from the straight line it would follow if there were no forces acting on it " because of its _____ it "falls around " around the earth

away - tangential force

____- a concentration of mass resulting from gravitational collapse, near which gravity is so intense that not even light can escape.

black hole

the orbital paths of the earth and the moon are ___ rather than ____

elliptical circular

Gravitational force between the Moon and the Earth is stronger on the side of the Earth nearer the Moon, and it is weaker on the side of the earth that s farther from the moon. simply because ___is weaker with increased distance.

gravitational force

2) halfway to the center of the earth, would the force of gravity on you be less than at the surface of the earth?

gravitational force on you would be less, beavuse there is less mass of earth below you, which pulls you with less force. If the Earth were a uniform sphere of uniform density, gravitational force halfway to the center would be exactly half that at the surface. But, since earth's core is so dense , gravitational force halfway down would be somewhat more than half. Exactly how much depends on how earth's density varies with depth, which is information that is unknown today

3) Gravitational force acts on all bodies in proportion to their masses. Why, then, doesn't a heavy body fall fast than a light body?

heavy and light bricks fall with the same acceleration because both have the same ratio of weight to mass. Newton's second law (a=f/m) reminds us that greater the force acting on greater mass does not result in greater acceleration.

___ occur when the Moon and Sun are closest to the earth

highest spring tides

1) we see the moon falls around earth rather than straight into it. If the moon's tangential velocity were zero, how would it move?

if the moon's tangential velocity were zero, it would fall straight down and crash into Earth.

____- wherin the effect of a localized source spreads uniformly throughout the surrounding space: the electric field about an isolated electron, light from a match, radiation from a piece of uranium, and sound from a cricket. -- example: spray can when spray 1 area unit then its _____, when spray 4 area units, its ____ thick, when spray nine area units its _____, thick. The thickness of the paint decreases as the ______ of the paint increases. d is the distance between the ___ of masses of objects.

inverse square law -- 1 layer think, 1/4 thick, 1/9, distance squared. center

___- a law relating to the intensity of an effect to the inverse square of the distance from the cause intensity~ 1/ distance squared ____- follows an inverse square law, as do the effects of electric, magnetic, light, sound, and radiation phenomena

inverse- square law gravity

1) by how much does the gravitational fore between two objects decrease when the distance between their centers is doubled? tripled? increased tenfold?

it decreases to 1/4, 1/9, 1/100 the original value.

every body in the universe attracts every other body with force that , for two bodies, is directly proportional to the product of their masses and inversely proportional to the square of the distance separating them: formula ? m1 & m2 are the masses of the bodies and d is the distance between their ____ Thus greater the mass, ______ greater the distance, the ____

law of universal gravitation F= G m1 x m2 / d squared centers. greater the force of attraction between them, in direct proportion to the masses. weaker forces of actraction

if the sun, earth, and moon are exactly in line than we have _____, for the full moon passes into Earth's shadow

lunar eclipse

you weight depends not only on your ___, but also on your ___ from the center of the earth. Ex: at the top of a mountain, your mass is the same as it is anywhere else, but you __ is slightly less than it is on the ground level because your __ from earth's center is greater.

mass distance weight distance

____- tides that occur when the moon is midway between new and full, either direction. Tides due to the sun and the moon partly cancel, making the high tides lower than average and the low rides higher than average.

neap tides

high tides are lower than average and the low tides are not as low as average low tides. These are called ____

neap tides

1) we know that both the moon and the sun produce our ocean tides. and we know the moon plays a greater role because it is closer. Does its closeness mean that it pulls on the Earth's oceans with more gravitational force than the sun

no, the sun's pull is much stronger. gravitational pull weakens as the distance squared. full answer pg. 170

____ effectively supplies a support force and nicely provides weight. Example: elevator at stop- weight is normal - as elevator is going up your weight is ___. as elevator is going down your weight is ____. elevator free falls your weight is ____.

rotation - more. less. zero

____- are higher than average high tides and lower than average low tides. happens when the sun, earth, and moon are aligned, the tides due to the sun and the moon coincide.

spring tides

why doesn't the sun cause tides 180 times greater than lunar tides?

the answer has to do with key word: difference. because of the greater distance of the sun, the difference in its gravitational pull on opposite sides of the earth is very small.

a broader definition of ____ of something is the force it exerts against a supporting floor or a weighing scale.

weight

greater the distance from the earth's center, the less _____ of an object ex: a child who weighs 300 N at seal level will weigh only 299 N atop mt. Everest for greater distances, __ is less

weight force

____- being without a support force, as in free fall.

weightlessness

2) According to the equation for gravitational force, what happens to the force between two bodies if the mass of one of the bodies is doubled? if both masses are doubled?

when one mass is doubled, the force between it and the other one doubles. If both masses are double, the force is four times as much.

1) Suppose you stepped into a hole bored clear through the center or the earth and made no attempt to grab the edges at either end. Neglecting air drag, what kind of motion would you experience?

you would oscillate back and forth. If earth were ideal sphere of uniform density and there were not air drag, your oscillation would be what is called simple harmonic motion. Each round trip would take nearly 90 minutes.

The value of __ indicates that the force of gravity is very weak force. It is the ___ of the presently known four fundamental forces ( the other three are ___, _____ )

G weakest electromagnetic force and two kinds of nuclear force

_____- the influence that a massive body extends into space around itself, producing a force on another massive body. It is measured in newtons per kilogram (N/KG) ---> the strength of earth's ____ , like its strength of forces on objects, follows the ____. It is strongest near Earth's __ and weakens with increasing ___ from the Earth.

Gravitational Field- gravitational field- inverse-square law- surface- distance

1) if there is an attractive force between all objects, why do we not feel ourselves gravitating toward the buildings in our vicinity?

Gravity does pull us to massive buildings and everything else in the universe. the forces between buildings and us are relatively small because their masses are small compared with the mass of the earth. The forces due to the stars are extremely tiny because of their great distances from us. These tiny forces escape our notice when they are overwhelmed by the overpowering attraction to the earth.

1) In what sense is drifting in space far away from all celestial bodies like stepping down off a stepladder?

In both cases, you'd experience weightlessness. Drifting in deep space, you would remain weightless because no discernible force acts on you. Stepping from a stepladder, you would be only momentarily weightless because of a momentary lapse of support force

_ is called the universal gravitational constant. F= G m1 m2 / d sqaured

G

____ - are caused by differences in the gravitational pull between the Moon and the Earth on opposite sides of the Earth

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