Physics Chapter 9

Flashcard maker : Lily Taylor
Isaac Newton synthesized _______.
terrestrial and cosmic laws
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. Newton’s second law of motion, F=ma, means that for a particular force F, the product mass x acceleration must always be the same. Therefore if mass is larger, acceleration must be smaller, and vice versa.
What is the Newtonian synthesis?
The union of terrestrial laws and cosmic laws
State Newton’s law of universal gravitation in words. Then do the same with one equation.
The force is proportional to the product of two masses and inversely proportional to the square of the distance between their centers: F ~ m1m2/d2.
What happens to the force of attraction between two planets when the masses of both are doubled?
The 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?
10 N
When G was first measured by Henry Cavendish, newspapers of the time hailed his experiment as the “weighing Earth experiment.” Why?
With a known mass, a scale, and the radius of Earth, you can calculate the unknown mass of Earth if you know G.
The constant G in Newton’s equation _______.
makes the units of measurement consistent
How does the thickness of paint sprayed on a surface change when the sprayer is held twice as far away?
It is ¼ as thick.
Where do you weigh more: at the bottom of Death Valley or atop one of the peaks of the Sierra Nevada? Why?
You weigh more in Death Valley because you are closer to the center of Earth.
What happens to the force of attraction between two planets when the distance between them is doubled?
The force decreases to one quarter.
Would the springs inside a bathroom scale be more compressed or less compressed if you weighed yourself in an elevator that was accelerating upward? Downward?
More compressed while accelerating upward, but less compressed while accelerating downward
Would the springs inside a bathroom scale be more compressed or less compressed if you weighed yourself in an elevator that was moving upward at constant velocity? Downward at constant velocity?
There would be no more compression and no more expansion for both upward and downward motion.
When is your weight measured as mg?
For a non-accelerating mass near the surface of Earth
Why are occupants of the International Space Station weightless?
They are in free fall.
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.
Why does the gravity in the Space Shuttle compare with the gravity on Earth the way it does?
The Space Shuttle is about the same distance from the center of the Earth than from the surface 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.
Suppose you are in an elevator. As the elevator starts upward, its speed will increase. During this time when the elevator is moving upward with increasing speed, your weight will be __________.
greater than your normal weight at rest
Suppose you are in an elevator that is moving upward. As the elevator nears the floor at which you will get off, its speed slows down. During this time when the elevator is moving upward with decreasing speed, your weight will be __________.
less than your normal weight at rest
As you found in Part A, your weight will be greater than normal when the elevator is moving upward with increasing speed. For what other motion would your weight also be greater than your normal weight?
The elevator moves downward while slowing in speed.
If you are standing on a scale in an elevator, what exactly does the scale measure?
the force you exert on the scale
Do tides depend more on the strength of gravitational pull or on the difference in strengths? Explain.
Tides depend only on the difference.
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.
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.
What is the magnitude of the gravitational field at Earth’s center?
Zero N/kg
If the mass of Earth somehow increased with no change in radius, your weight would
increase also.
If the Sun were twice as massive
both of these
You experience weightlessness
momentarily when you step off a chair.
in a freely falling elevator.
in the absence of a supporting surface.
Earth’s gravitational field extends
both inside and outside Earth and throughout the entire universe.
The direction of a gravitational field is
in the same direction as gravitational attraction.
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.
The amount of gravitational force that acts on a space vehicle while in Earth orbit is
nearly as much as the vehicle’s weight on Earth’s surface.
Rate this statement: No force due to Earth’s gravity acts on astronauts inside the orbiting space station.
always false
How far must one travel to escape Earth’s gravitational field?
forget it; you can’t travel far enough.
The force of gravity acting on you will increase if you
stand on a planet with a shrinking radius.

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