Chapter 9 physics gravity
A 150 pound person decides to move to the center of the earth( carving out a little cavity for her house). What is the net force of gravity exerted by the earth on this person? Much less than 150 pounds but greater than zero 0 pounds 150 pounds
0 pounds. Since there is the same amount of material in all directions, at equal distance from the person, the net force is zero
A person weighs 150 pounds. He is standing on a scale inside an elevator. If the elevator is free falling downward (perhaps the cable broke) what is the reading of the scale?
0 pounds. The person is in free fall so his acceleration is -9.8 m/s/s and thus the only force acting on him is that of gravity
What is the magnitude of Earth's gravitational force on a 1-kg body at Earth's surface?
10 N
A 150 pound astronaut is inside the space shuttle, orbiting around the Earth just above the Earth's atmosphere (the atmosphere's thickness is very small compared to the radius of the Earth). The force of gravity acting on the astronaut A) is roughly 150 pounds. B) Around 120 pounds C) 0 pounds.
A) is roughly 150 pounds.. even though the astronaut is in a state of free fall and feels weightless, the force of gravity is still the same as if he were standing on earths surface
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.
spring tides
During the new Moon or full Moon, the effects of Moon and Sun add up, causing more pronounced
When is your weight measured as mg?
For a non-accelerating mass near the surface of Earth
A person weighs 150 pounds. He steps in an elevator and stands on a scale. If the elevator is moving upwards with a constant speed, what is the reading of the scale?
Greater than 150 pounds Less than 150 pounds 150 pounds 150 pounds, since the elevator is not accelerating, the scale provides an upward force equal in magnitude to the force of gravity
A person weighs 150 pounds. He is standing on a scale inside an elevator. The elevator is moving downward and slowing down (coming to a stop) what is the reading of the scale?
Higher than 150 pounds. Since the elevator is slowing down while moving downwards, the person is accelerating upwards
What happens to the strength of the gravitational field at the surface of a star that shrinks?
It increases.
What is a gravitational field, and how can its strength be measured?
It is a force field on any body with mass. Its strength is the force per unit mass on a test mass.
How does the brightness of light change when the source is held twice as far away?
It is ¼ as bright.
The reason the Moon does not crash into the Earth is that the
Moon has a sufficient tangential speed
How did Einstein view the curved path of a planet?
Moving in curved 4-dimensional spacetime
Unique experiments can be carried out in the Space Station because of the lack of gravity.
No, the uniqueness of the experiments is not due to the lack of gravity but due to weightlessness
Suppose a rocket ship, while sitting on Earth, has a weight of 10,000 N. The rocket ship takes off and reached a distance from Earths center of 3R Earth. What is the force due to gravity acting on the spaceship?
Roughly 1,100 N. The force of gravity here is 1/9th that when on the surface
A person weighs 150 pounds. He is standing on a scale in an elevator and stands on a scale. The elevator is accelerating upwards at a rate of 10 m/s/s what is the reading of the scale?
Roughly 300 pounds. The upward force of the scale minus the force of gravity is equal to the mass time acceleration. Since the acceleration is roughly g(9.8 m/s/s), this means that the upward force needs to be 2mg
Why does the gravity in the Space Shuttle compare with the gravity on Earth the way it does?
The Space Shuttle and the surface of the Earth are about the same distance from the center of the Earth.
Why do the astronauts in the Space Shuttle float around?
The Space Shuttle is in free fall, so the shuttle and the astronauts inside it are continuously falling toward the Earth. They thus experience apparent weightlessness.
Both the Moon and the Sun produce our ocean tides, but the tides are primarily due to the Moon. Why?
The difference in lunar pulls is greater than the difference in solar pulls.
Suppose you weigh 400 pounds and want to weigh only 100 pounds. Instead of going on a diet, you could live in space. How far from the center of the earth would you have to live?
The distance would be two earth radii away from the center of the earth. Since the distance to the center of the earth doubled, the weight would decrease by a factor of four
State Newton's law of universal gravitation in words.
The force is proportional to the product of two masses and inversely proportional to the square of the distance between their centers.
How does the force of gravity between two bodies change when the distance between them is halved?
The force quadruples.
What happens to the force of attraction between two planets if their masses are doubled and the distance between them is also doubled?
The force would remain the same.
How does the gravity in the Space Shuttle compare with the gravity on Earth's surface?
The gravity in the Space Shuttle is approximately equal to the gravity on the surface of the Earth.
What did Newton discover about gravity that was not known at the time?
The law of universal gravitation The Newtonian synthesis The equation for the force of gravity All of the above all of the above
Predict how the upward force exerted on the feet by the scale will compare to the man's weight if the elevator is moving downward at a constant speed.
The upward force on the feet will be equal to the man's weight.
Predict how the upward force exerted on the feet by the scale will compare to the weight of the man if the elevator is moving upward at a constant speed.
The upward force on the feet will be equal to the man's weight.
Predict how the upward force exerted on the feet by the scale will compare to the man's weight if the elevator is accelerating downward.
The upward force on the feet will be less than the man's weight.
Predict how the upward force exerted on the feet by the scale will compare to the man's weight if the elevator is accelerating upward.
The upward force on the feet will exceed the man's weight.
Why it is not possible to directly observe or photograph a black hole?
Their gravity is so strong that nothing, not even light, can escape a black hole.
Why are occupants of the International Space Station weightless?
They are in free fall.
Do tides depend more on the strength of gravitational pull or on the difference in strengths? Explain.
Tides depend only on the difference.
neap tides
When the Moon is halfway between a new and full Moon, the tides due to Sun and Moon partly cancel each other, causing less pronounced
Where do you weigh more--at the bottom of Death Valley or atop one of the peaks of the Sierra Nevada? Defend your answer.
You weigh more in Death Valley because you are closer to the center of Earth.
How could your weight be greater than mg? How could your weight be zero? Give examples.
Your weight is greater than mg when you are accelerating upward. Your weight is zero when you are in free fall
What is the magnitude of the gravitational field at Earth's center?
Zero N/kg
If you weigh yourself in an elevator, the scale will indicate the greatest weight when the elevator
accelerates upward
No force due to Earth's gravity is acting on the astronauts inside the orbiting space shuttle. This statement is:
always false
Surrounding a magnet is a magnetic field. Surrounding an electron is an electric field. Surrounding Earth is
an alteration in space in which mass experiences a force, and a gravitational field.
If the Sun suddenly collapsed and became a black hole, without changing its mass, the Earth would
continue to circle in its usual orbit
If Earth's radius somehow increased with no change in mass, your weight would
decrease
According to Newton, doubling the distance between two interacting objects
divides by 4 the gravitational force between them.
Newton's most celebrated synthesis was and is of
earthly and heavenly laws
Einstein's theory of gravitation, compared with Newton's
eliminates the role of force
When you stand in an elevator accelerates upward, compared with your rest weight your weight reading on a scale is
greater
Each of us weighs a tiny bit less inside the ground floor of a skyscraper than we do on the ground away from the skyscraper. The reason for this is the
mass of the building attracts us upward slightly
when at rest on the launching pad, the force of gravity on the space shuttle is quite huge- the weight of the shuttle. when in orbit, some 200 km above earths surface, the force of gravity on the shuttle is nearly as much about half as much nearly zero zero
nearly as much
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
none of these 𝟐𝒎𝟏𝒙 𝟐𝒎^2/ (2d)^2
The force of gravity acts on all apples on an apple tree. Some apples are twice as far from the ground as others. For the same mass these twice-as-high apples have
practically the same weight
Which pulls on the oceans of Earth with a greater force?
sun. Because of the Sun's great distance, the difference in gravitational pulls on opposite sides of Earth is very small. In other words, the Sun pulls almost as hard on the far side of Earth as it does on the near side
When an object moves away from the surface of Earth, the gravitational force decreases because
the distance between Earth and the object increases
newtonian synthesis
the same set of laws apply to both celestial and terrestrial objects
Of the four fundamental forces presently known, the force of gravity is
the weakest
