FREE ESSAY ON GRAVITY

GRAVITY

Gravity
The gravitational force at the surface of the planet is the force that binds all bodies
to earth, this force is one of the four forces recognized by physicists, and this kind of
force is known as "gravity" it attracts every celestial object to earth, and though it is
the most important of the forces essential for our lives, it is the least comprehended of
them all
Throughout ages scientists have tried to solve the mystery of gravity, and one of the
first discoveries concerning gravity was made by Aristotle who concluded from his
experiments that the downward movement of any body is that has weight had a proportional
relationship between its quickness in motion and its size. However this theory was
accepted for centuries, but after a series of experiments made by Galileo, Aristotle's
theory was proved to be incorrect, as Galileo said after a series of experimenting at the
Pisa tower that bodies of different sizes fall with the same speed. Later on, the idea
that the force is needed so as to change the motion of the body was discovered. After
that a great scientist was to improve all the previously accepted theories, this
scientist was Newton who was to make decisive advances in understanding gravity. In his
first law Newton said that a body in state of rest or uniform motion in a straight line
will keep on moving unless acted upon by a force, while in his second Newton expressed
his first law in a more quantitative way as he said that force acting on a body is the
rate of change of it's momentum which can be put in a rule as 
F= ma
Where (F) is the force acting on the body while (a) and (m) are the acceleration and
inertial mass of the body respectively.
Newton also made the law of gravitation in which he expressed the gravitational force of
attraction between any two bodies acting along the line joining them as
Where (m) is the mass of the two bodies and (r) is the distance between them, while (G)
is the proportionality constant known as the constant of gravitation, afterwards Newton
made his very important assumption in which he showed that the inertial mass of a body is
identical to its gravitational mass which implied that the gravitational force exerted on
or by an object is directly proportional to its inertia.
After that, scientists wanted to determine the value of the gravitational constant, in
which the English scientist Henry Cavendish calculated as 
G= 6.754 x 10 Nm /Kg 
For hundreds of years, Newton's laws where considered as the basis of modern physics, and
one of the things that proved Newton's theories was the discovery of the planet Neptune
but there were also many important issues that were not discovered by Newton such as,
that there is no way to describe mass except with reference to acceleration, another
issue is that no force moves without acceleration, a third one is that when we mention
acceleration we have to say with respect to what? .
All the previously mentioned theories, were studied by Einstein who wondered why is the
inertial mass proportional to the gravitational mass and after experimenting he made his
theory of equivalence in which stated that if we had two systems, the first had
acceleration with no gravitational field while the second has acceleration with no
gravitational mass and while the other is at rest and has a gravitational field, the
results would be equivalent, and by the year 1916 Einstein had completed the mathematical
theory of gravitation which was the general theory of relativity. Einstein's theories
opposed those of Newton's in at least two major and measurable issues that were the
curvature of light and the shifting of the wavelength of the light.
In conclusion, the issue was a subject of research done by the greatest scientists ever
known as Newton and Einstein, and it will always be a subject of research, as think the
gravitational mystery still might not be totally unraveled and I think that many other
theories will be made to emphasize the force that keeps standing at that planet.