chapter9 Flashcards
What happens to the force of attraction between two planets when the masses of both are doubled?
force quadruples
What is the magnitude of the gravitational force between two 1-kg bodies that are 1 m apart?
6.67 × 10 -11 N
What is the magnitude of Earth’s gravitational force on a 1-kg body at Earth’s surface?
10N
How does the force of gravity between two bodies change when the distance between them is doubled?
The force decreases to ¼ of its initial value
Describe how the gravitational forces from the Sun and the Moon compare from one side of Earth to the other.
The Sun exerts a stronger force on the side of Earth nearest the Sun, and the Moon exerts a stronger force on the side nearest the Moon.
According to Newton, the greater the masses of interacting objects, the
greater the gravitational force between them.
According to Newton, when the distance between two interacting objects doubles, the gravitational force is
1/4
If Earth’s radius somehow increased with no change in mass, your weight would
decrease
If the mass of Earth somehow increased with no change in radius, your weight would
increase also
A very massive object A and a less massive object B move toward each other under the influence of gravity. Which force, if either, is greater?
both forces are the same
Two objects move toward each other due to gravity. As the objects get closer and closer, the force between them
increases
The force of Earth’s gravity on a capsule in space will lessen as it moves farther away. If the capsule moves to twice its distance, the force toward Earth becomes
1/4
The force of Earth’s gravity on a capsule in space increases as it comes closer. When the capsule moves to half its distance, the force toward Earth is then
four times greater
When the distance between two stars decreases by one-third, the force between them
increases to nine times as much
A weight watcher who normally weighs 400 N stands on top of a very tall ladder so she is one Earth radius above Earth’s surface. How much is her weight there?
100 N
Which is most responsible for Earth’s ocean tides?
moon
The main reason ocean tides exist is that Moon’s pull is stronger
on water closer to it than on water farther away
Tidal forces in general are the result of
unequal forces acting on different parts of a body.
One side of the Moon continually facing Earth is
tidal lock
Calculate the force of gravity on the 1-kg
mass if it were 3.2×10^6m
above Earth’s surface (that is, if it were one and a half Earth radii from Earth’s center).
4.3 N
Why are all tides greatest at the time of a full Moon or new Moon?
At full Moon and new Moon, the tides from the Moon and the Sun add because they are in line with Earth
Which two factors mainly affect ocean tides on Earth?
the moon and the sun
Consider Earth and the Moon. As you should now realize, the gravitational force that Earth exerts on the Moon is equal and opposite to that which the Moon exerts on Earth. Therefore, according to Newton’s second law of motion __________.
the Moon has a larger acceleration than Earth, because it has a smaller mass
In what sense does the Moon “fall”?
It falls away from the straight path that it would follow if there were no forces acting on it.
Which has the higher tides: spring tides or neap tides? Why?
Spring tides are higher, because the tides from the Moon and Sun add together.
If Earth shrank, but there was no change in its mass, then what would happen to your weight at the surface?
increase
Earth’s gravitational field is strongest at _______.
Earth’s surface
Why is a black hole invisible?
The escape velocity of the black hole is greater than the speed of light.
Einstein’s theory of gravitation, compared with Newton’s, _______.
eliminates the role of force
From the viewpoint of an observer in the orbiting rocket, what happens to time on the other rocket as it falls toward the event horizon of the black hole?
Time runs increasingly slower as the rocket approaches the black hole.
As the falling rocket plunges toward the event horizon, an observer in the orbiting rocket would see that the falling rocket __________.
slows down as it approaches the event horizon and never actually crosses the event horizon
you know that from afar you’ll never see the in-falling rocket cross the event horizon, yet it will still eventually disappear from view. Why?
Its light will become so redshifted that it will be undetectable.
If you were inside the rocket that falls toward the event horizon, you would notice your own clock to be running __________.
at a constant, normal rate as you approach the event horizon
If you were inside the rocket that falls toward the event horizon, from your own viewpoint you would __________.
accelerate as you fall and cross the event horizon completely unhindered
Black holes are essentially _______.
collapsed stars
What is the force of gravity on a 500-N woman standing on Earth’s surface?
500 N
Two planets in space gravitationally attract each other. If both the masses and distances are doubled, the force between them is
none
Tides caused mainly by the Moon occur in Earth’s
oceans.
interior.
atmosphere
The concept of force is fundamental to
Newton’s theory of gravitation
An asteroid exerts a 360-N gravitational force on a nearby spacecraft. If the spacecraft moves to a position three times as far from the center of the asteroid, the force will be
40 N
When a star collapses to form a black hole, its mass
remains the same
