Universal gravitation Flashcards
Newton compared motion of the moon to a
cannonball fired from the top of a high mountain.
What would happen if the tangential velocities of the planets were reduced to zero?
Their motion would be straight toward the sun and they would indeed crash into it.
What theory of the solar system did Newton’s theory of gravity confirm?
Copernican theory
Newton’s law of universal gravitation states that
every object attracts every other object with a force that for any two objects is DIRECTLY PROPORTIONAL TO THE MASS OF THE OBJECT
What did Newton discover about gravity?
the same force that caused an apple to fall from a tree was also the force that kept the moon in place. (me not sure)
NOTE: F IS INVERSELY PROPORTIONAL TO THE SQUARE OF D MEANS
IF D INCREASES BY A FACTOR OF 3, F DECREASES BY A FACTOR OF 9
The greater the object distance from Earth’s center
the less an object will weigh
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 were twice as tall, would the
force of gravity on the apple be only 1/4 as
strong?
No, 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 Earth (6370 km) before the weight of the apple would reduce to 1/4 N.
How does the force of gravity change
with distance?
Gravity decreases according to the inverse square law
note: The field lines are closer together where the gravitational field is stronger.
Any mass in the vicinity of Earth will be accelerated in the direction of the field lines at that location.
Earth’s gravitational field follows the inverse-square law.
Earth’s gravitational field is strongest near Earth’s surface and weaker at greater distances from Earth.
What kind of field surrounds Earth and causes objects to experience gravitational forces?
Gravitational field (this is zero at the center of the earth)
In a cavity at the center
of Earth, your weight
would be?
zero, because you would be pulled
equally by gravity in all
directions.
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, approximating simple harmonic motion. Each round trip would take nearly 90
minutes.
Describe the gravitational field of Earth
at its center.
gravity is zero because all the mass around you is pulling “up” (every direction there is up!)
The condition of weightlessness is not the absence of ______ but the absence ______
gravity. support force
