Conceptual Physics Chapter 13

True or false ( black hole: Its volume is unchanged from the star from which it collapsed

F

T of F: Newton believed that the mass of the moon affects how it falls.

False

T or F: Isaac Newton discovered gravity?

False

True of False: The law of universal gravitation is a complicated law that only describes a few unique instances.

False

True or False: two bodies have to be in contact for a force to be exerted.

False; the Earth and the moon exert force on each other without actually being in contact.

what happens if the mass of one object decreases by half?

The the force is divided by 2 (multiplied by one half)

What happens if the distance between the objects' centers of mass decreases by half?

The the force is multiplied by 4.

Explain why lakes have almost no tides

There is no significant difference in the moon's pull on different parts of the lake

What was the cause of perturbations discovered in the orbit of Planet Uranus?

There was a disturbing body beyond the orbit of Uranus (Neptune)

Black holes are near the centers of most galaxies. How do these black holes affect stars near them

They cause the stars to speed around in tight orbits

Why are there no large objects in the solar system today with very low tangential velocities?

They crashed into the sun a long time ago.

T or F: ? Newton's theory of gravity confirmed the Copernican theory of the solar system.

True

T or F: At the top of a mountain, your weight is slightly less than at ground level.

True

T or F: The moon falls beneath the straight line it would follow if no force acted on it.

True

When are field lines closest together?

Where the field is strongest

True of False? The gravitational influence of every object is exerted through all space.

Yes, bc Newton proved gravitational pull is universal.

If you stepped into a hole bored completely through Earth and made no attempt to grab the edges at either end, what kind of motion would you experience.

You would oscillate back and forth, basically simple harmonic motion.

What is G?

a constant

Define gravitational field

a force field that exists in the space around every massive body

What is the weight on a scale when an elevator is accelerating downwards

less than usual

The solar and lunar tides coincide

spring tide

High tides are higher than usual, and low tides are lower than usual.

spring tides

True or false: (black hole)The configuration of the gravitational field around it represents a collapse of space itself

t

Who first measured G

the English physicist Henry Cavendish

Define perturbation

the deviation of an orbiting object from its path around a center of force, caused by the action of an additional center of force

What happens when the mass of one object doubles?

the force is multiplied by 2

Why is the tidal influence on a close object greater than it is on one far away.

the inverse square law drop in gravitational force gives a greater ratio of the force on the near side of the object to that on the far side.

what does G describe

the strength of gravity

G is better known as

the universal gravitational constant

T or F: Circular motion is accelerated motion, which requires a force.

true

True of False; The pull of the moon and Earth on each other causes them both to be slightly elongated rather than spherical

true

How often does a tide occur?

twice per day (every 12 hours)

Pressure against the Earth is something we interpret as _____...

weight

Do the great lakes have tides

yes, because they are so huge

What would happen is you fell into a hole bored through the Earth

you acceleration would diminished because the mass above you partly cancels the pull below.

What is the weight of a rock at earth's center?

zero because there isn't a gravitational field

The sun's pull on Earth is_____ times greater than the moon's pull on Earth.

180

Newton compared motion of the moon to a cannonball fired from the top of a high mountain. Describe the possible paths for the cannonball proposed by Newto

A cannonball fired with a small horizontal speed would follow a parabolic path and soon hit Earth. If the speed were faster, the path would be less curved and the cannonball would hit Earth farther away. At a fast enough speed, the path would become a circle and the cannonball would circle indefinitely

Explain Newton's calculation that the moon falls 1.4 millimeters each second.

An apple falls about 5 m in its first second of fall. The moon is about 60 times farther from the center of Earth than an apple at Earth's surface. The moon should fall 1/(60)2 of 5 m, or 1.4 millimeters in one second.

How are gravitational field lines related to the acceleration of an object around Earth?

Any mass near Earth will be accelerated in the direction of the field lines at that location.

Why doesn't the moon hit the Earth as it falls in orbit?

Because it has enough tangential velocity to stay in orbit.

Why are people often unaware that gravity accelerates us?

Because we are almost always in contact with the Earth

What do field lines show?

Field lines show the strength and of direction of the force field

Explain why Earth is round

Gravity caused Earth to attract itself together before it became solid. Any "corners" of Earth have been pulled in so that Earth is a giant sphere.

What is the inverse square law?

If one quantity is multiplied by a factor, another quantity decreases by the square of that factor.

Explain why a star that is at least two to three times more massive than our sun will eventually collapse into a black hole.

It is so massive that its collapse will not stop and its density will become infinite.

What will happen during the fusion process of the sun

It will expand to become a red giant

What would happen to the motion of a planet if its tangential velocity were reduced to zero

It would crash into the sun

Explain how a black hole that is part of a binary pair can be detected, even though it cannot be seen

Matter streams from the visible star of the binary pair toward the black hole, emitting X-rays that can be detected by telescopes.

True of False: (black hole) Its gravitational field beyond the original radius of the star is unchanged.

T

Why is the moon the dominant tidal force?

The Moon is the dominant tidal influence because the fractional difference in its force across the Earth is greater than the fractional difference seen from the Sun. This difference in force follows the inverse square law.

What happens if the distance between the objects' centers of mass doubles

The force is divided by 4

explain tides

The gravitational pull of the moon is stronger on the ocean water nearest the moon and weaker on the opposite side, causing a bulge on each side. As Earth spins, a fixed point moves under both bulges each day.

Why does the moon fall towards the Earth?

The moon is pulled by Earth's gravity.

What causes the size of the sun?

The result of a tug of war between two opposing processes; nuclear fusion and gravitational contraction

Newton realized the moon must be falling _____ the Earth

around

how does gravity weaken

as the square of distance

Where is the Earth's gravitational field zero?

at Earth's center

Explain what will cause our sun to collapse some 5 billion years from now.

bc it will essentially to run out of school

When our sun no longer gives off heat and light, it will be a

black dwarf

What causes ocean tides

differences in the gravitational pull of the moon on opposite sides of the Earth. The moon's attraction is stronger on Earth's ocean closer to the moon and weaker with the increased distance. The different in pulls across Earth slightly elongates it. Then the Earth rotates and there are two sets of ocean tides per day.

What is the equation for universal gravitation?

f= G(m1)(m2)/d^2

T or F: there is no gravity in space

false gravity is literally everywhere

The gravitational field of an object causes them to experience

gravitational forces

What is the weight on a scale when an elevator is accelerating upwards

greater than usualy

As the sun collapses, a different type of fusion will begin in which ____ fuses into ____ .

helium fuses into carbon

What direction is the tangential velocity that keeps the moon from hitting the Earth

horizontal/sideways

What type of fuel ls needed for the type of fusion that currently takes place in the sun

hydrogren

Occurs when the moon is halfway between a new moon and a full moon.

neap

The solar and lunar tides do not overlap

neap tide

The pulls of the moon and sun are perpendicular to each other.

neap tide (neap = 90)

Suppose that an apple at the top of a tree is pulled by Earth's gravity with a force of 1 N. If the tree was twice as tall what would the force of gravity on the apple be?

no because the twice as tall apple tree is not twice as far from Earth's center the taller tree would have to have a height equal to the radius of the Earth before the weight of the apple would reduce to 1/4 of a newton.

What is the weight on a scale when an elevator is falling freely

no weight

Can light escape a black hole

nope

What is the weight on a scale when an elevator is sitting still

normal weight

A tidal effect causes the solid surface of Earth to rise and fall as much as ______ meter twice each day

one-quarter

Occurs at times of a new or full moon.

spring

Occurs when the sun, Earth, and moon are all lined up.

spring tide