## Introduction to Gravity

In physics, gravity is the universal force of attraction that operates between all matter. Gravitation was discovered by Newton in the year 1665, when he saw an apple falling down the tree. It is by far the weakest known force in nature and so has no bearing on the intrinsic characteristics of common matter. On the other hand, it influences the trajectories of bodies in the solar system and elsewhere in the universe, as well as the architecture and evolution of stars, galaxies, and the entire cosmos, due to its extended reach and ubiquitous activity. Each body on earth has a weight, or downward force of gravity, proportional to their mass, which is exerted by the mass of the earth.

### What is Gravity ?

Gravity is the force that pulls items toward the centre of a planet or other entity. All of the planets are kept in orbit around the sun by gravity. Gravity exists in everything that has mass. Gravity is stronger for heavier objects. Gravity weakens with distance as well. As a result, the stronger the gravitational force of two things, the closer they are to each other. The gravity of the earth is caused by all of its mass. Its whole mass exerts a cumulative gravitational force on the entire mass of your body. That is what gives you heft. And if you were on a planet with a lower mass than earth, you would weigh less. The value of gravity on the surface of earth is 9.8 m/s^{2}.

### What Causes Gravity ?

In his theory of relativity, Sir Albert Einstein postulated that gravity is more than a force. According to him gravity is a curvature in the space-time continuum. Because the rubber sheet is distorted by the large ball's weight, this description is commonly seen as a heavy ball lying on a rubber sheet, with smaller balls sinking in towards the heavier object. Although the curvature of space-time cannot be observed directly in reality, it may be seen in the movements of things. Because the space it is travelling through is bent toward that object, every object under the influence of another celestial body's gravity is influenced.

### What is Gravitational Force ?

Newton's law of gravity is used to describe gravitational force. It states that everyone in the universe attracts every other body with a force proportional to the product of their masses and inversely proportional to their distance. Gravitational pull is all around us. Consider two point mass bodies C and D of masses m_{1} and m_{2.} Let r be the distance between their centres and F be the gravitational force of attraction between them and mathematically it is given as,

F=G m_{1}m_{2}/r^{2}

Here G is the universal gravitational constant.

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### Gravitational Force Examples in Our Daily Lives

There are various types of daily life examples which are based on gravitational force and help us in building the gravity concepts. Some daily life examples are,

**The Objects' Stability:** The objects on the earth's surface do not levitate or float in the air. This is due to the gravitational pull that exists between the items and the earth. Unless disrupted by an external force, the cup on the table does not float in the air and remains in the same spot. Gravity is also in charge of holding other items in place.

**Formation of Tides:**** **Tides are the periodic rise and fall of water in seas over a short period of time. These huge waves in the waters are created by the gravitational attraction of the moon and sun on the water present in the oceans. The oceans would be calmer in the absence of gravitational attraction because the magnitude of the tides would be reduced to one-third of their previous height.

**Falling of Feather:** A feather is an extremely light body that floats in the air. This light feather, on the other hand, gradually falls to the earth. The gravitational pull is exclusively responsible for this. A similar effect may be observed with any other light body, such as a piece of paper.

**Walking:** Walking is one of the most prevalent physical behaviours observed in practically every living terrestrial species. We do not float or perform levitation when walking since our feet are in close contact with the earth. Gravity, the ultimate phenomena, assists us in walking.

### Application of Gravitational Force

The various applications of gravitational force are as follows,

This is used to compute the gravitational attraction of the planets in the cosmos.

It is also used to calculate the trajectory and anticipate the motion of celestial bodies.

It attracts all objects to the ground.

If there are no obstacles in the route, rocks and other things put on a slanting surface tend to roll down. The rolling of any physical body occurs as a result of gravitational force.

Drinks placed into a glass remain at the bottom and do not rise to the brim. This is made possible because of the application of gravitational force.

## FAQs on Gravity on Earth

Q1. What is the value of gravitational force between earth and moon if mass of moon is 7.36 × 10^{22 }kg, mass of earth is 5.96 × 10^{24} kg and they are separated by a distance of 3.8 × 10^{8} m ?

**Ans: **To solve this problem we have to apply the formula of gravitational force of attraction. In the question we are provided with the mass of moon (M_{m}=7.36 × 10^{22} kg), mass of earth (M_{E}=5.96 × 10^{24} kg and distance between them i.e, r=3.8 × 10^{8} m. In this case we can write the expression of gravitational force is,

F=G M_{m}M_{E}/ r^{2}

Here G is the gravitational constant and its value is 6.67 × 10^{-11}Nm^{2}/kg^{2}.

Now putting the values in the above expression as,

F=(6.67 × 10^{-11}N m^{2}kg^{-2}× 7.36 × 10^{22}kg × 5.96 × 10^{24}kg)/(3.8 × 10^{8}m)^{2}

After solving the above expression we obtain,

F=(292.58 × 10^{35}Nm^{2})/(14.44 × 10^{16}m^{2})

Upon dividing the numerator and denominator terms we get,

F=20.26 × 10^{19}N

Hence, the approximate value of gravitational force between earth and moon is 20.26 × 10^{19}N.

Q2. Which two factors determine the force of gravity?

**Ans:** The force of gravity mainly depends upon the mass of the objects and the distance between them. The mass of the objects is the first component that influences the amount of gravity acting on each of them. The greater the mass, the greater the gravitational pull that one object exerts on the other. The distance between the two objects is the second component that influences the amount of gravity on each object. The greater the distance between two objects, the less gravitational pull each object exerts on the other. This indicates that the greater the distance between two objects, the greater the gravitational pull on one of them.