What is Gravity? The Force that Keeps Us Grounded

spacetime curvature caused due to gravity

Gravity or gravitation is a force exerted by anything and everything that has mass. Albert Einstein’s General Theory of Relativity explains the phenomenon of gravity in the most accurate way. According to this theory, mass of an object creates a curvature in the spacetime and this curvature causes pulling of the other objects. More massive the object, higher would be the gravity.

Definition of Gravity: Gravity is the force that attracts a body towards the center of the earth, or towards any other physical body having mass.

How does the Gravity Work?

Technically, gravity is not really a force but rather an effect of the curvature in spacetime. Although, even an atom possess some amount of gravity, but to be able to exert perceivable gravitational pull, an object has to be huge. The following image shows how an object creates a warp in the spacetime and how this creates gravity. The image also shows how objects with grater mass create larger curvature.

spacetime curvature caused due to gravity

Examples of Gravity

Gravity of Earth

The most apparent effect of gravity is that we remain grounded on Earth. When we jump, we do not simply go off the face of the Earth. Instead we fall back on the ground. Earth’s gravitational pull keeps us, all other plants, animals, oceans’ water etc. grounded. There would not be any gravity in Earth, everything that’s not fastened to the ground will fly off into the space. World’s oceans will become empty as all the water will fall into the space.

Solar System

Solar system is a system of planets, satellites and other celestial bodies orbiting around the star named, Sun. Gravity is responsible for holding this whole system in place. Sun’s gravity is so strong that it keeps all the planets orbiting around it. Gravity of planets, in turn, keeps hold on their respective satellites.

Tides in Ocean

Gravitational pull of Earth’s only natural satellite, the moon, causes high and low tides in oceans. Moon pulls the ocean’s water towards it causing high tides. As a consequence the other areas in the ocean witness a low tide.

Our Weight on Earth

It is important to understand that weight and mass are two different things. Weight is actually a measurement of the gravitational force acting on an object. So, if something weighs 1 kg on Earth, the same thing will weight 0.16 kg on moon because moon has lesser gravity than the Earth. Similar, the same object will weigh 2.36 kg on Jupiter because the Jovian planet has higher gravity than the Earth. Every object becomes weightless (but not massless!) in the outer space because there exists no gravity.

image showing difference between mass weight

Newton’s Law of Universal Gravitation

Sir Isaac Newton, the great English mathematician and physicist, postulated that every particle attracts every other particle in the universe with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. This is called the Newton’s Law of Universal Gravitation.

Formula to Calculate Gravitational Force

F = G (m1 x m2 / r2)
where F is the gravitational force acting between two objects, m1 and m2 are the masses of the objects, r is the distance between the centers of their masses, and G is the gravitational constant.

Earth’s Gravitation Constant

Earth’s gravitational constant (or gravitational pull / force) is equal to 9.807 m/s²

This basically means that an object being pulled by Earth’s gravity will accelerate toward Earth’s center at the rate of 9.807 meters per second.

Gravitational Waves

In 2015, advanced LIGO detectors, found the evidence that gravitational waves are a reality. These waves are generated and move through spacetime, when two extremely massive bodies (like two black holes or neutron stars) collide and merge with each other. Gravitational waves travel through spacetime at the speed of light.

Gravity of Black Hole

A black hole is essentially extremely high mass packed in a very small space. Because gravity is directly proportional to the mass of an object, the gravity of a black hole is so high that nothing can escape its pull. If anything will go close enough and cross a limit called the event horizon, that entity will not be able to resist the gravitational pull of black hole. Even light can not escape a black hole — this is the reason a black hole is completely black.

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