Gravitation is the force that holds us all down to the surface of the earth. Anything thrown upwards falls back to the earth. It is not only the earth that has the pull of gravity but also every thing else in the universe. Everything in this universe attracts every other body to itself.
Early scientists believed that the speed with which an object hits the ground from any height depended on the weight of the object. It was Galileo, who made a serious effort to study the force of gravity. He went to the top of the Leaning Tower of Pisa and dropped objects of different weights. He showed that objects heavy and light when dropped together reached the ground at the same time. He proved that they had the same constant acceleration.
In another experiment, Galileo rolled a ball down a slope. With this he proved that a body moving on a perfectly smooth horizontal surface would neither speed up not slow down.
Sir Isaac Newton, the English physicist and mathematician laid the foundation of modern physics. It was the who discovered the law of gravity. As a young boy while sitting under an apple tree he began to wonder why objects always fell down instead of going up. His mind dwelled on this subject for a long time. As he grew older he started to investigate the phenomenon of gravitation. Finally in 1685 Newton expounded the Universal Law of Gravitation.
According to this law, all objects fall to the earth with the same acceleration regardless of mass. He wrote down in great detail his observations and theories with mathematical calculations. His famous book, Principia, was published with the aid of Edmond Halley, the English astronomer who financed it.
Much later Albert Einstein attempted to explain what is gravity. His theory was a very complicated one that required a very scientific mind to understand it. As science has taken leaps and bounds in the field of astronomy we now know that the force of gravity is 6 times more on the earth than on the moon. The planet of Jupiter has a still stronger force of gravity. A person on that planet would weigh three times more than he would on the earth.
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