What is gravity and how does it work?
Gravity is a very important force. Gravity or gravitational forces are forces of attraction. It's like the Earth pulling on you and keeping you on the ground. That pull is gravity at work. Every object in the universe that has mass exerts a gravitational pull, or force, on every other mass. The size of the pull depends on the masses of the objects. Like the Earth and Moon, the gravitational pull becomes very impressive. The gravitational force between the Earth and the molecules of gas in the atmosphere is strong enough to hold the atmosphere close to our surface. Smaller planets, that have less mass, may not be able to hold an atmosphere.
The Sun's gravitational pull keeps our planet orbiting the Sun. The motion of the Moon is affected by the gravity of the Sun and the Earth.
Aryabhata first identified the force to explain why objects do not fall when the earth rotates, Brahmagupta described gravity as an attractive force and used the term "gurutvakarshan" for gravity.
As for the science behind the action, we know that Isaac Newton defined gravity as a force - one that attracts all objects to all other objects. We know that Albert Einstein said gravity is a result of the curvature of space-time. These two theories are the most common and widely held (if somewhat incomplete) explanations of gravity.
For hundreds of years, Newton's theory of gravity pretty much stood alone in the scientific community.
That changed in the early 1900s. Albert Einstein, who won the Nobel Prize in Physics in 1921, contributed an alternate theory of gravity in the early 1900s. It was part of his famous General Theory of Relativity, and it offered a very different explanation from Newton's Law of Universal Gravitation. Einstein didn't believe gravity was a force at all; he said it was a distortion in the shape of space-time, otherwise known as "the fourth dimension".
How does it work?
Every time you jump, you experience gravity. It pulls you back down to the ground. Without gravity, you'd float off into the atmosphere.
The theory states that each particle of matter attracts every other particle (for instance, the particles of "Earth" and the particles of "you") with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
The standard formula for the law of gravitation is:
Gravitational force = (G * m1 * m2) / (d2)
Where G is the gravitational constant, m1 and m2 are the masses of the two objects for which you are calculating the force, and d is the distance between the centers of gravity of the two masses.
G has the value of 6.67 x 10E-8 dyne * cm2/gm2. So if you put two 1-gram objects 1 centimeter apart from one another, they will attract each other with the force of 6.67 x 10E-8 dyne.
A dyne is equal to about 0.001-gram weight, meaning that if you have a dyne of force available, it can lift 0.001 grams in Earth's gravitational field. So 6.67 x 10E-8 dyne is a minuscule force.
When you deal with massive bodies like the Earth, it adds up to a rather powerful gravitational force. Because of that, we all are not floating around in space right now.
The force of gravity acting on an object is also that object's weight. The formula to determine weight is:
Weight = m * g
Where m is an object's mass, and g is the acceleration due to gravity. Acceleration due to gravity on Earth is 9.8 m/s² -- it never changes, regardless of an object's mass.
That's why to drop a pebble, a book, and a couch off a roof, they'd hit the ground at the same time.
Gravity not only pulls on mass but also on the light. Albert Einstein discovered this principle. If you shine a flashlight upwards, the light will grow imperceptibly redder as gravity pulls it. You can't see the change with your eyes, but scientists can measure it. Black holes pack so much mass into such a small volume that their gravity is strong enough to keep anything, even light, from escaping.
Every object in space exerts a gravitational pull on every other, and so gravity influences the paths taken by everything traveling through space. It is the glue that holds together entire galaxies. It keeps planets in orbit. It makes it possible to use human-made satellites and to go to and return from the Moon. It makes planets habitable by trapping gasses and liquids in an atmosphere. It can also cause life-destroying asteroids to crash into planets.
In December 2012, a research team in China announced that it had produced measurements of the phase lag of Earth tides during full and new moons which seem to prove that the speed of gravity is equal to the speed of light.
That means if the Sun suddenly disappeared, the Earth would keep orbiting it normally for 8 minutes, which is the time light takes to travel that distance. The team's findings were released in the Chinese Science Bulletin in February 2013.
In October 2017, the LIGO and Virgo detectors received gravitational wave signals within 2 seconds of gamma-ray satellites and optical telescopes seeing signals from the same direction. This confirmed that the speed of gravitational waves was the same as the speed of light.