## What is gravity?

Why people on the other side of the Earth do not fall off and float into space? Why we can't fly and birds can? The answer to both question is gravity. Gravity is an attracting force that exists because of the mass of the Earth. The word gravity comes from the Latin "gravitas", which means weight. The force of gravity is one of the four fundamental forces of nature. When Sir Issac Newton saw that apple from the tree fall to the ground, he started thinking about why it fell down. He was the first one to understand and explain gravity. In this article we shall discuss why does Earth have gravity.

## Effects of gravity

The effects of gravity cause objects to fall toward the Earth, like that apple that fell near Newton. It causes the water to run down hill from the mountains. Gravity gives weight to objects. Other effects of gravity are as follows:

- It makes you stand on the surface of Earth and not float away.
- It keeps the planets in their orbits
- It causes tides
- It provides you with a blanket of air making life possible.

## Theory of Gravity

Sir Isaac Newton in 1687 developed** **the Law of Gravitation, which stated that: Every particle of matter attracts every other particle of matter with a force proportional to the product of their masses and inversely proportional to the square of their distance apart. When written as an equation:

F=(G×M_{1}×M_{2}) / (d^{2})

Where F is the force of attraction due to gravity, G is a constant called as Universal Gravitational Constant, M_{1} and M_{2} are the masses of the two objects, and d is the distance between them.

Thus, according to this law you are pulling the Earth toward you and the Earth is pulling you toward it. As the mass of the Earth is much much larger than your mass, you are pulled strongly toward the Earth and this pull is called as gravity.

So gravity comes from mass and the more mass an object has, the more gravity it will exert.

Newtonian Law of Gravitation was considered absolute for nearly 200 years and remained undisputed, however Leverrier discovered a discrepancy in the orbit of planet Mercury which could not be explained even after considering the possibility of another unknown planet in vicinity. This particular discordance was explained by Einstein's General Theory of Relativity in 1916.

## Other Articles on Gravity

Nature of Gravity is space is an excellent article on the origins of gravity and traces it to the Big Bang.

Understanding the Surface Gravity of Planets is an article on the gravity of all the planets in our Solar System.

## References

Gravitation in New Standard Encyclopedia Volume six by Standard Educational Corporation, Chicago

https://physics.about.com/od/classicalmechanics/a/earthgravity.htm?rd=1

https://math.ucr.edu/home/baez/physics/Relativity/GR/gravity.html

https://www.simplegravity.com/

McGraw – Hill Concise Encyclopedia of Science & Technology Edited by Sybil P. Parker

Image of Earth from: https://commons.wikimedia.org/wiki/File:Earth-Erde.jpg