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.

Force (What is Force)

Force
Let consider, a object or a book lying on the desk. It does not move or continuous to be lying on that desk forever at the same position until somebody displace it to the other places or position. For moving that book somebody have to either pull and push it. Then such pull and push on a body or a object is called Force. Therefore it is clear that force is must be applied to body to bring the body into motion to rest and rest to motion. Similarly, "Force is an agent which tries to change the body condition from motion to rest or rest to motion."
Let assume that the ball is rolling on the rough ground . We can see that the ball stops after covering the certain distance. It takes longer and longer time to stop on the smooth ground as that rough ground. So, we can well assume that when the ground is perfectly smooth then the ball would continue moving forever in the same direction with a constant speed. It is the roughness of the surface which provides opposing force called Friction, which tries to stop the ball from moving. So to bring a body into rest to motion, force has to act on it in opposite direction of its motion. In the another word, Force is that push or pull on a body that changes or tends to change the state of rest or of uniform motion in a straight line.
Force action on a body can do the following things
1. It can change the shape of the body .
2. It can change the speed of the body.
3. It can change the direction of motion of the body.

Balanced and UnBalanced Forces
When the forces are given to as body if the body do not change its state of rest or of motion states then the given forces are called Balanced Force. For example ; If two persons are pulling the rope in opposite forces then the rope does-not move in any side and the rope remains steady. Thus, the two forces act by the persons on the rope are Balanced Forces in this case.
When the forces are given to as body if the body changes its state of rest or of motion states then the given forces are called Unbalanced Force. For example ; If a person pulls the object towards the west then the object also moves towards the west. If again it pulled towards the North then it moves towards the North. Then, this force act on object are Unbalanced forces in this case. This unbalanced forces produces motion.

Inertia
Inertia is the property of a body due to which it remains to remains in state of motion or of rest in a straight line without unbalanced force can only change the state of rest to motion and vice-versa because it opposes any change in its state of rest or of uniform motion in a straight line.
Inertia may show itself as the following three forms:
1. Inertia of Rest
2. Inertia of Motion
3. Inertia of Direction

1. Inertia of Rest
It is the property of a body by virtue of which it remains to be still n state of rest until the unbalance force is act on the body.
Example:
a) When we are standing in the bus if the bus suddenly starts then we fall backwards because at first our whole body is in rest. When the bus suddenly starts then our lower part of the bus comes to motion but the upper part remains in rest due to inertia of rest.
b) When we hit the blanket then the dust particles falls down. This is because at first both dust particles and the blankets are in rest position. When we hit the blankets then it comes into motion but the particles remains rest due to inertia.

2. Inertia of Motion
It is the property of a body by virtue of which it remains to be still in the same as in motion unless unbalanced force are act on in it.
Example:
a) We are standing in a moving bus. When it suddenly stops then we falls forward. This is because at first both parts of our body are in motion. When bus suddenly stops then our lower part comes in rest but upper part remains in motion due to inertia of motion.
b) An athletic runs for some distance before taking a long jump. Because by running for some distance he/she gains more inertia of motion which helps him/her to take a long jump.

3. Inertia of Direction
It is the property of a body by virtue of which maintains to maintain its direction of motion until unbalanced forces are act on it.
Example:
a) When a moving bus suddenly takes turns then the people sitting in the bus, they experience a jerk in the outward direction. This is because the people tend to maintain their original direction of motion due to inertia of direction.
b) When the wheel rotates at a high speed then the mud which is sticking at the wheel files off tangentially. This is due to inertia of direction.

VECTOR
Those quantities which have both magnitude and direction are called vectors. Some examples of vector are Velocity, Acceleration, Force, Displacement, etc. The sum of vectors may be zero, position and negative. They are added by certain vector rules. Vector is simply represented by letter 'A' or by letter bold letter P.

SCALARS
Those quantities which have only magnitude but not direction are called scalars. Some examples of scalars are Distance, Speed, Work, etc. The sum of Scalar are always position number. they are added by the simple rules and it is simply represented by letter 'a' and P.

DISTANCE
The actual path or length which traveled by the body is known as distance. It is scalar quantity. Its S.I. unit is meter (m). A body should covered between initial and final position. The net distance covered cannot be zero.

DISPLACEMENT
The shortest distance which is between the initial position and final position is known as displacement. It is a vector quantity. It is also measured in S.I. system in meter (m). The net displacement may be zero.

SPEED
The distance traveled per unit time is known as speed. It is a scalar quantity. It is always positive. It is represented by V letter. Its S.I. unit is measured in m/s.

VELOCITY
It is defined as the distance covered by a body per unit time. Its S.I. unit is m/s. It is vector quantity because it has both magnitude and direction and can be positive and negative.