What is gravity

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(No Transcript)
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What is gravity?
Galileo and Newton gave the name gravity to the
force that exists between the Earth and objects.
Newton showed that the same force exists between
all objects.
Even today, no one knows exactly why objects
attract each other.
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link1, link2, link3

• The paths of the planets are ellipses with the
  center
• of the sun at one focus.
• An imaginary line from the sun sweeps out equal
  areas
• in equal time intervals. Thus, planets move
  fastest
• when closest to the sun, slowest when farthest
  away.
• The ratio of the squares of the periods of any
  two
• planets revolving about the sun is equal to
  the ratio
• of the cubes of their average distances from
  the sun.

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link1, link2, link3
In 1666, Isaac Newton determined that the same
force that kept the planets in motion must also
exist between every object.
He stated that every object in the universe
attracts every other object in the universe. The
force of attraction between two objects is
directly proportional to the product of their
masses, and inversely proportional to the square
of their separation distance.
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In equation form
m1
m2

F
G
d2
F is the force of attraction, measured in
NEWTONS, between masses m1 and m2
G is the Universal Gravitation Constant, equal to
6.67 x 10-31 N m2/kg2
m1 and m2 are the attracting masses, measured
in KILOGRAMS
d is the distance between their centers of mass,
and is measured in METERS
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The Earths gravitational attraction provides
the centripetal force needed to keep a satellite
in orbit.
The linear velocity v needed to keep a satellite
in a circular orbit a distance r above
the Earths surface is given by
(
)
1/2
G
Me
v

r
v is in meters/sec
Me is the mass of the Earth in kilograms
r is in meters
G is the Universal Gravitation Constant
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A gravitational field exists around every
object that has mass.
The gravitational field always points directly
toward the objects center of mass.
The magnitude of the field is given by
F
g

m
g is the field strength, measured in
Newtons/kilogram
m is the test mass, measured in kilograms
F is the force of attraction, measured in
Newtons, on the test mass