Answer 3:
The force of gravity between two objects
depends on the mass of the two objects and the
square of the distance between them.
F =
Gm_{1}m_{2}/r^{2}
G is the gravitational constant
(6.674×10^{−11} N m^{2} kg−2¬)\
m_{1} is the mass of the first object
m_{2} is the mass of the second object
r is the distance between the centers of mass of
the objects
If the objects are very massive, then the
gravitational force between them will be very
strong, but if they are far apart, it will be
weak. Since the distance, r, in the equation is
squared, it has a stronger effect on the force
than the mass of an object.
The gravitational force between the Earth and
a 50 kg (110 lbs) person standing on the Surface
of the Earth is ~500 N (a Newton, N, is a unit
of force). The Sun is 333,000 times more massive
than the Earth (more mass increases
gravitational force), but it is also 150 million
kilometers away (distance decreases
gravitational force). Since distance is more
important in determining gravitational force,
the force between the Sun and a person on the
surface of the Earth is much smaller than
gravitational force the Earth exerts on that
person. It is so small (only 0.06% of the force
from the Earth) that you would never notice it
in every day life. The force a person feels from
the Moon is even smaller, 0.00035% of the
gravitational force from the Earth, and the
force from Jupiter when it is closest to the
Earth is even smaller yet, only 0.0000037% of
the force from the Earth.
The gravitational force between the Sun and
the Earth is about 3.54x10^{22} N.
This force keeps the Earth orbiting around
the Sun. The gravitational force from the
other planets does slightly affect the Earth’s
orbit, but the gravitational pull from the other
planets and the Moon is still very small. The
gravitational pull of the Moon on the Earth is
only 0.55% of the gravitational force between
the Sun and the Earth. When they are closest to
the Earth, Jupiter only exerts 0.0062% of this
force and Mars only 0.00023%.
References:
http://solarsystem.nasa.gov/planets/index.cfm
http://nssdc.gsfc.nasa.gov/planetary/factsheet/
http://en.wikipedia.org/wiki/Newton%
27s_law_of_universal_gravitation
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