GRAVITATIONAL FORCE(what is this?)

GRAVITATIONAL FORCE
If we released a object from a height then the object falls downwards. Not only the object all the living and non-living things falls downwards. Why does the object fall towards the earth? And why does it not go upwards? These question led by Isaac Newton to think about falling body while he was sitting under the apple tree and apple fallen down in 1666 A.D. Later in 1687 A.D., he found out that the earth attracts the object towards its center. So, the body falls from the height towards its center the earth due to the force of attraction of the earth. He also found that not only the earth, other object of this universe attracts the other object. He called this force as Gravitational Force.
Gravitation, the force of attraction between all objects that tends to pull them toward one another. It is a universal force, affecting the largest and smallest objects, all forms of matter, and energy. Gravitation governs the motion of astronomical bodies. It keeps the moon in orbit around the earth and keeps the earth and the other planets of the solar system in orbit around the sun. On a larger scale, it governs the motion of stars and slows the outward expansion of the entire universe because of the inward attraction of galaxies to other galaxies. Typically the term gravitation refers to the force in general, and the term gravity refers to the earth's gravitational pull.

Consequences of gravitational force
1. The planets revolve round the sun in uniform motion due to presence of gravitational force.
2. There is presence of atmosphere on the earth due to gravitational force.
3. Water falls from upper level to lower level due to gravitational force.
4. Tides in seas and oceans are due to the gravitational force.
5. The gravitational force of earth keeps firmly on the surface of the earth.

According to the Newton’s Law of Gravitation Force
It state that, "The force of attraction between two heavenly bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres." It is called universal law because it is applicable to the entire universe. The gravitational force between two objects can be expressed by the following equation: F= GMm/d2 where F is the gravitational force, G is a constant known as the universal constant of gravitation, M and m are the masses of each object, and d is the distance between them. Newton’s law affects all objects in the universe, from raindrops in the sky to the planets in the solar system. It is therefore known as the universal law of gravitation.

Universal Gravitational Constant 'G'
The value of G is same for any pair of masses in the universe but the value of G doesn’t depend on the nature or properties of the medium in which the masses are placed. So, that's why the value of G is constant everywhere in universe. So, it is called Universal Gravitational Constant.
Thus it is a force between unit masses separated by 1 meter distance. This S.I. unit of it is Nm2/kg2. Its value is 6.67*10-11 Nm2/kg2.

Gravity/Weight of a Body
The force which pulls an object towards the center of a planet is called gravity.Its S.I unit is Newton(N)/weight of a body.It is measured by W=GMm/R2

Gravitational Field
It is defined as the area around the earth or the planet up to where it can pull the object.In practice the gravitation field may become to weak to be measured beyond a particular distance.In theoretically the gravitation field extend up to infinity.

Gravitation field Intensity
It is defined as the gravity that applies to an object of 1 kg mass present on the surface of that planet.It is denoted by (I).Its S.I unit is N/kg.
Gravitation field Intensity=Force experienced/Mass.
i.e.I=F/M. We can find I by following
F=GMm/d2
F/m=GM/d2 (i.e.I=F/M)
i.e.=GM/d2 or GM/r2.

Acceleration due to Gravity
When a body is released from a significance height it freely falls towards the surface of the earth due to gravity of earth. Thus,When a body falls freely,it has an acceleration due to Gravity of earth.Hence, The acceleration produced in freely falling object towards surface of the earth due to the influence of gravity is called acceleration due to Gravity.It is denoted by g and its S.I unit is NM/s2. It's value is 9.8 m/s in earth.

Free fall
When an object is falling towards the surface of the earth only under the influence of gravity without external resistance, the fall of the object is called free fall. Falling objects accelerate in response to the force exerted on them by Earth’s gravity. Different objects accelerate at the same rate, regardless of their mass. This illustration shows the speed at which a ball and a cat would be moving and the distance each would have fallen at intervals of a tenth of a second during a short fall.
The fall of an object towards the earth's surface only under the influence of gravity without external resistant is called free fall. But there is presence of atmosphere around the surface of the earth which creates external resistance. Therefore, the fall of parachute towards earth's surface is not a free fall.

Weightlessness
weightlessness is a condition at the weight of an object of certain mass becomes zero.Weightlessness, state of not experiencing the effects of gravity.

For information on:

• forces at work, see Gravitation: Acceleration; Free Fall; Thematic Essay: Physics, from Leonardo to Hertz
• studies by astronauts, see picture, Space Shuttle Astronaut Experiencing Weightlessness, in Aerospace Medicine: Space Medicine; Astronaut: What Do Astronauts Do?; Roberta Lynn Bondar; Space lab; Vostok Program: Introduction
• biological effects of weightlessness, see Aerospace Medicine: Physiological Findings; Osteoporosis
• reducing effects of weightlessness, see Space Exploration: Salyut Space Stations
• video of astronauts experiencing weightlessness, see video, Playing in Space, in Space Shuttle: Later Missions
• neutral buoyancy in sport diving, see Diving (underwater): Training and Certification.