Newton’s Law of Universal Gravitation
Every object in the Universe attracts every other object with a force
directed along the line of centers for the two objects that is proportional
to the product of their masses and inversely proportional to the square
of the separation between the two objects.
It was Newton who reasoned that the same force that causes an apple to fall
from a tree causes the Moon to “fall” in its circular orbit.
It was Newton who reasoned that the force that exists between all masses in
the universe is directly proportional to the product of their masses.
It was Newton who reasoned that the force of attraction between two masses
got smaller as the distance between the masses gets larger – to be more
specific, the force of gravity is inversely proportional to the square of the
distance between the objects.
It was Newton who reasoned that masses attract other masses from their
center of mass (this is why we feel a force of gravity when standing on the
Earth’s surface – the center of mass of the Earth is its center.
Newton was aware of the gravitational constant G, but its exact value was
determined later as our ability to measure motion improved.