# why do we have gravity on earth

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:
Where F is the force of attraction due to gravity, G is a constant called as Universal Gravitational Constant, M 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 in 1916. Our third grade class has been studying gravity and the motion of objects. We had a question: If the Earth no longer had gravity, would buildings and other structures attached to the Earth float away? We would like to start our answer by saying that we're sure you realize that this could never happen. The Earth has mass, just like every other solid object does (including you). It is the Earth's mass that causes it to have gravity, and so in order to not have gravity the Earth would have to not have mass. But if the Earth didn't have mass, it wouldn't be there anymore! Having said that, though, let's now imagine that we could magically turn off the gravity while leaving the Earth behind. What would happen to the things on Earth depends on how they are attached.

As you know, the Earth is rotating at quite a speed (you're moving at over a thousand miles per hour at the equator due to the Earth's rotation alone). Now if you spin something around your head on a string, it goes around in a circle until you let go of the string. Then it flies off in a straight line. If the circle is very big, then at first the straight line is almost the same as the circle -- however, after a short amount of time, the two paths will be very different, since the circle bends around but the straight line does not. "Switching off" gravity is analogous to letting go of the string. Things not attached to the Earth in any other way would fly off into space in a straight line that would take them away from the surface of the Earth. In buildings, people would start floating gently upwards until they bumped into the ceiling. Outdoors, however (or in buildings with GIANT ceilings), things would start floating away from the Earth gently but eventually go much faster, as their straight lines took them farther and farther away from the circular path that the spinning Earth takes.

The Earth's atmosphere itself would also float off into space, for the same reason! Some things (like trees and most buildings) are rooted into the Earth. They would not fly off because they are being held down. In fact, the force you would need to hold on and keep yourself from flying away from the Earth is very weak, only about 0. 3% as strong as the force of gravity (and even weaker away from the equator). However, things which are holding on to the Earth would eventually have problems too -- the Earth itself would most likely break apart into chunks and float off into space, since it is only held together by gravity also! Anyway, we hope that you enjoyed the answer. Like we said to start with, though, you should remember that this could never happen! This page was last updated on June 27, 2015.

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