Everything in the universe moves even if the motion or movement may be in a small amount or very slow. Evenif we stand still, the Earth is moving around the Sun, and the Sun is moving around our galaxy and the movement never stops. Motion is one part of Mechanics. Scientists discovered several rules or laws that explain motion and the causes of changes in motion. Newton’s three Laws of motion and Law of gravitation are very important among them.
In1687, the English physicist Isaac Newton made the link between stars which attract each other and the objects which fall to earth. The famousapple falling from a branch on to Newton’s head brought him this revelation about gravitation. According to him, the objects could be twostars or an apple and the earth. In fact, the earth pulls a lot more strongly upon the apple than the Universe and the apple also pulls equally on our earth. But, the enormous difference in mass between the apple and the earth makes the action which the apple has on the earth negligible (but not nothing or it is not zero). All of these occur as ifthe mass of objects was concentrated at their centre, called the centreof gravity.
Theastronomical Universe is dominated by the law of gravitation: Two objects in space attract each other so much more strongly when they are massive and closer together.
The following formula is used to calculate the Gravitational Force of attraction, according to Newton’s Law of gravitation.
F = GMm /d2
where F the gravitational force of attraction or gravitational force,
G the Universal gravitational constant
d the distance between the earth of mass M and the object of mass m.
Gravityor gravitational forces are forces of attraction and it is like the Earth pulling us and keeps us on the ground. And this pull is gravity atwork. Every object in the universe which has mass exerts a gravitational pull, or gravitational force, on every other mass. The gravity motion or the motion due to the gravitational force or the gravity or the size of the pull depends on the masses of the objects. One exerts a gravitational force on the people around him/her, but that force is not very strong, since people are not much massive. When we look at objects of large masses, like the Earth and Moon etc. the gravitational pull or gravity motion becomes very impressive. The gravitational force between the molecules of gas in the atmosphere and the Earth is so strong to hold the atmosphere close to earth’s surface. Smaller planets with lesser mass may not be able to hold an atmosphere since its gravitational force will be less as comparison.
Try this Physics Formula Sheet which might help you to solve physics problems.