Gravity

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What is Gravity?

What is the force that holds us down on the Earth and stops us from flying up in space? If you know the answer to this question then you know what is gravity. Gravity is one of the universe’s fundamental forces that dominate every moment of our conscious existence. It helps us to walk on the ground, pulls the basketballs and baseballs back to the ground, and gravity is also something our muscles cannot struggle against. The story of gravity goes together with the story of physics and many famous physicists have found ways to figure out what causes gravity.


What is Gravitation?

Scientists have defined four types of forces in the universe that either attract or repel an object from another. These are:

  • Strong force

  • Electromagnetic force

  • Weak force

  • Gravity

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Of these 4 types of forces, strong and weak forces operate within the center of an object’s atoms. The EM force applies to objects that have an excess of charge (electrons, protons) like socks that shuffle over a fuzzy carpet.


Gravity is the force that acts upon objects having mass. It is an all-pervasive force that keeps our foot on the ground yet it is still a puzzle for many and the answer to the question what do you mean by gravity.


What do You Mean by Gravitational Force

Gravity can be defined as the force which a planet (or a body) exerts on other objects and draws them towards its center. It is this force of gravity that keeps all the planets in their orbits around the Sun.


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Newton explained what is meant by gravitational force in his law of universal gravitation as a force of attraction that exists between any two objects having mass. This force is directly proportional to the masses of the objects and inversely proportional to the distance between them. It is mathematically expressed as:

F = G * (m1 m2) / R

Where F - Force of gravity.

G - Gravitational constant and its value is 6.67 x 10-11  N * m2/kg2.

R - The distance between the objects.


What is Gravity Made of

Earth’s gravity comes from its entire mass. Earth’s entire mass exerts a combined gravitational pull on your body mass. It is this gravitational pull of the earth which gives you your weight. So if you are on a planet whose mass is less than the earth, then you would weigh less there. You and earth both exert gravitational force on each other, but since earth’s mass is way more than your weight, your force has no effect on the planet.


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A team of scientists based in the South Pole discovered the celestial fingerprint using a telescope, BICEP2. This fingerprint explains the beginning of time and reveals microscopic details of gravity. Quantum particles in an infant universe gave rise to “inflation,” which is the reason behind why the universe exploded outwards.


It also revealed that gravity is made up of quantum particles called gravitons. A single graviton is too small and massless, but these gravitons' quantum fluctuations in the infant universe bend pockets of this tiny space-time.


What is the Gravitational Force of Earth

The gravity of the earth is denoted by g and is defined as the net acceleration that is induced in objects owing to the gravitation (mass distribution within the earth) and centrifugal force due to the earth’s rotation.


Earth’s acceleration due to gravity is 9.8 m/s2 close to its surface (also called 1 g). Gravity decreases as the distance from the Earth increases.


Gravity on Earth is Not the Same Everywhere

The Sun’s gravity keeps the Earth in such a position that we can enjoy the sunlight without being burnt. Gravity holds our entire atmosphere and the air we breathe in, so living without gravity is impossible for us.


But the force of gravity is not the same at all parts of our planet Earth. There is more gravity in the places where there is more mass underground compared to places with less underground mass. The force of gravity is also dependent on where you are standing, near the equator, or further from it. This is due to Earth rotating on its axis; hence, the force of gravity at the equator is less (9.789 m/s2) than the gravity at the poles (9.832 m/s2). This means you would weigh slightly more at the poles than at the equator due to the centripetal force.


NASA has deployed 2 spacecrafts that measure these variations in Earth’s gravity. These spacecrafts are part of GRACE (Gravity recovery and climate experiment).


GRACE can detect small changes in gravity over time and has revealed crucial details about Earth. As an example, GRACE monitors sea level, and changes in it can make it determine changes in Earth’s crust brought upon by earthquakes.


Examples of Gravity

Some interesting examples of gravity are:

  • Gravity is the weakest force amongst all the fundamental forces known. A bar magnet can pull a paperclip upwards due to electromagnetic force, which is stronger than the gravitational pull of the whole earth on that paper clip.

  • It is gravity due to which a car coasts downhill even when you are not stepping on the gas.

  • Gravity holds the earth and all the planets around the Sun in their proper positions and orbits.

  • The force of gravity holds gases inside the Sun.

  • Tides in the oceans are led by the force of gravity of the moon.

  • The stars and planets have been created by gravity, which has pulled together the materials they are composed of.

  • Gravity not just pulls masses, but it affects light as well. Einstein proved this fact. If you send a flashlight upwards, it turns red with time due to gravitational pull. This color change is not perceptible by us, but scientists have been able to measure it.

FAQ (Frequently Asked Questions)

Q1. What is the Connection Between Gravity and Black Holes?

Ans 1: A black hole is an astronomical object with an area of immense gravity as a lot of mass is packed into a small volume. Nothing can escape from a black hole owing to its strong gravitational force. It stops even light from escaping it. The surface of black holes is called event horizons. They define the boundary where the escape velocity needed to escape its gravitational pull is greater than the velocity of light. This is the cosmos' speed limit; hence matter and radiation can fall in a black hole but cannot come out of it.


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Q2. Differentiate Between Gravity and Gravitational Force.

Ans 2: Mostly people would think of gravitational force and gravity as one and the same, but there are little differences between the two.


Gravity:

  • It is the force that Earth exerts on any object near it.

  • It is always an attractive force.

  • It is towards the earth’s center.

  • It requires only one mass.

  • The force of Gravity is zero at the center of the earth.

Gravitational Force:

  • It is the force acting between any two objects having masses.

  • This could either be an attractive or repelling force.

  • Its direction is towards the radial distance between the masses.

  • It requires two masses.

  • The gravitational force between 2 objects is zero if they are separated by an infinite distance.