 # Gravity

## What is Gravity?

We barely think about gravity in our daily lives, but we must realize that it defines the way we interact with the world. We grow within its constraints, and our heart, muscles, balance system all depend on it. Gravity is also known as Gravitation which is the universal force of attraction acting between all matter. Gravity is the mysterious force that makes everything fall down towards the Earth. We can define gravity as:

A force that attracts a body towards the centre of the earth, or towards any other physical body having mass. ## History of Gravity

• In 1687, Sir Isaac Newton first discovered gravity. While sitting under an apple tree, he noticed an apple falling down. Then he tried to figure out why the apple instead of going up or left or right, came down. In this situation, there was clearly an unknown force at play, that force is what Newton called gravity and his theory is called Newton’s law of Universal Gravitation.
• Later in the early 20th century, Albert Einstein developed a whole new idea about gravity. According to him, gravity is the warping of space and time. ## Gravity Formula

Issac Newton defined the force of gravity as follows:

Every particle of matter in the universe attracts every other particle with a force that is directly proportional to the product of the masses of the particles and inversely proportional to the square of the distance between them.”

Mathematically, this translates to:

 $F=G\frac{m_{1}m_{2}}{r^{2}}$

Where,

• F is the force,
• $m_1$ and $m_2$ are masses of the objects interacting
• r is the distance between the centre of the masses
• G is the gravitational constant (6.674×10−11 m3⋅kg−1⋅s−2)

This equation gives the magnitude of the force and since it is an attractive force it will always be directed towards the other object. From the above equation, we can come to the conclusion that anything that has mass has gravity. Objects with heavier mass have more gravity. The closer the two objects are, the heavier the gravitational pull between them. Gravity gets weaker with distance. The above formula is used to calculate the gravitational force between two objects. ## Examples of Gravity

A few examples of gravity at work are:

• The gases in the sun are held together by gravity.
• Gravity is responsible for water to rest at the bottom of a glass instead of hovering over at the top of the glass.
• The force of attraction between the earth and the moon causes tides in the ocean. This is the result of gravity.
• Gravity causes the moon to revolve around the earth.

Gravity has the same effect on all objects. If you drop an iron road and a feather, they will fall at the exact same speed. Due to the effect of air resistance on gravity, it might look like the iron rod falls at a greater speed. However, if they were dropped in the vacuum, they would fall at the exact same time. The gravity of an object depends on its size. To be more specific, the Gravity of an object depends on the mass of that object. It is undoubtedly the weakest known force in nature and thus plays no role in determining the internal properties of everyday matter.

## Importance of Gravity

When we jump, why do we land on the ground? Why don’t things stay up when you throw them?

An unobservable force that pulls objects towards each other. Earth’s gravity is what makes things fall and keeps you on the ground. It is because of gravity, we can walk on the ground otherwise we would have been flying all around. Gravity helps objects to stick to the ground. Gravity is the only reason due to which there is a proper distance between earth and sun.

### How Weight is Related to Gravity? Weight is defined as the force with which a body is attracted towards the earth by gravitation. It is just another word for the force of gravity Fg. Weight is a force that acts on all objects near earth. The weight of an object can be calculated by multiplying the mass of the body with the magnitude of the acceleration due to gravity (g = 9.8 m/s2).

Mathematically, it is represented as:

 Fg = mg

Where,

• Fg is the force of gravity
• m is the mass of the object
• g is the acceleration due to gravity

Many people confuse mass with weight. One has to keep in mind that mass is the measure of how much the body resists velocity, in other words, the inertia of the object. Although they are closely related to each other, they mean different things. The mass has units of kg, whereas, the weight being a force has units of N.

• The best current estimate of G is that it equals about $6.67259\times 10^{-11}$ newton-square meter per square kilogram.