In the realm of physics, the letter ‘g’ holds significant importance as it represents the acceleration due to gravity. This fundamental concept is essential for understanding the behavior of objects under the influence of Earth’s gravitational pull. In this guide, we will delve deep into the definition, nature, and measurement of ‘g’ and explore its relation to the universal gravitational constant ‘G.’ Let’s embark on a journey to unravel the mysteries behind ‘g’ in the fascinating world of physics.

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Understanding ‘g’ – The Acceleration due to Gravity

In physics, ‘g’ refers to the acceleration experienced by a free-falling object under the influence of Earth’s gravitational force. It is often denoted as 9.8 m/s^2, which is the approximate value of acceleration on Earth’s surface. This numerical value plays a crucial role in various physical phenomena, including motion, force, and energy.

Deriving the Relationship between ‘g’ and ‘G’

Newton’s Universal Law of Gravitation

Before we explore the relationship between ‘g’ and the universal gravitational constant ‘G,’ let’s briefly recap Newton’s universal law of gravitation. According to this law, any two objects with mass exert an attractive force on each other. The force of attraction is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

Newton’s Second Law of Motion

Newton’s second law of motion states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. Mathematically, it can be expressed as:

F = m * a

where F is the net force, m is the mass of the object, and ‘a’ is the acceleration.

Relating ‘g’ and ‘G’

Now, let’s establish the relationship between ‘g’ and ‘G.’ If an object is falling freely under the influence of gravity, the acceleration it experiences is ‘g.’ On the other hand, the universal gravitational constant ‘G’ represents the force of attraction between two objects with unit mass separated by a unit distance.

To relate ‘g’ and ‘G,’ we consider the following equation:

F = G * (M * m) / R^2


  • F is the force of attraction between two objects,
  • G is the universal gravitational constant,
  • M is the mass of the massive body (e.g., Earth),
  • m is the mass of the falling object, and
  • R is the radius of the massive body.

Substituting ‘g’ into the Equation

Since the object is falling freely due to gravity, its acceleration is ‘g.’ Therefore, we can substitute ‘g’ into the equation as follows:

F = m * g

Equating the Forces

Equating the force of attraction (F = m * g) with the gravitational force (F = G * (M * m) / R^2), we get:

m * g = G * (M * m) / R^2

The Constant Nature of ‘G’ and the Independence of ‘g’

One crucial aspect to note is that ‘G’ is a constant value (approximately 6.67 x 10^-11 Nm^2/kg^2) and remains the same at any point in the universe. This means that the force of attraction between two objects with unit mass is consistent regardless of their location.

In contrast, ‘g’ varies depending on the location and mass of the massive body. For instance, the acceleration due to gravity on Earth is approximately 9.8 m/s^2, but it differs on other celestial bodies.

Measuring ‘g’ – Experiments and Applications

The value of ‘g’ can be measured through various experiments. One common method is by using a simple pendulum. By measuring the period of oscillation of the pendulum, we can calculate ‘g’ using the formula:

g = (4 * π^2 * L) / T^2


  • L is the length of the pendulum, and
  • T is the time period of one complete oscillation.

The acceleration due to gravity finds numerous applications in physics and engineering. Understanding ‘g’ is crucial for designing structures, calculating velocities of falling objects, and predicting the behavior of projectiles.

The Significance of ‘g’ in Space Exploration

In the context of space exploration, ‘g’ plays a crucial role in understanding the conditions on other celestial bodies. For instance, on the Moon, the acceleration due to gravity is only about 1/6th of that on Earth. This impacts the movement of astronauts and the design of spacecraft during lunar missions.


In conclusion, ‘g’ is a fundamental concept in physics, representing the acceleration due to gravity on Earth’s surface. It plays a pivotal role in various aspects of physics, from motion and force to space exploration. While ‘g’ and the universal gravitational constant ‘G’ are related, they are independent entities with different characteristics. Understanding ‘g’ enables us to comprehend the behavior of objects in the presence of Earth’s gravitational force, making it a cornerstone of physics and scientific exploration.


“G” or the Universal Gravitational Constant is related to gravity through Newton’s Universal Law of Gravitation. It represents the strength of the gravitational force between two objects with mass. The force of attraction is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

What is the Universal Gravitational Constant?

The Universal Gravitational Constant, denoted by “G,” is a fundamental constant in physics that appears in Newton’s law of gravitation. It quantifies the force of attraction between two objects with unit mass separated by a unit distance. The value of “G” is approximately 6.67 x 10^-11 Nm^2/kg^2.

Is the value of “G” constant?

Yes, the value of “G” is constant at any point in the universe. It remains the same regardless of the location or the masses of the objects involved in the gravitational interaction. This constancy is one of the essential characteristics of “G” and facilitates the accurate understanding of gravitational interactions.

How is “G” measured?

Measuring “G” is a challenging task and requires precise experimental techniques. One common method is the Cavendish experiment, which involves measuring the small gravitational attraction between two masses using a sensitive torsion balance. Several sophisticated variations of this experiment have been conducted over the years to determine “G” with high precision.

What are the units of “G”?

The units of the Universal Gravitational Constant “G” are Nm^2/kg^2, where N represents Newton (the unit of force), m stands for meters (the unit of distance), and kg denotes kilograms (the unit of mass). These units ensure that the gravitational force is appropriately calculated based on the masses and distances involved.

Why is “G” important in physics?

“G” is of paramount importance in physics because it underpins the understanding of gravitational interactions in the universe. It allows us to calculate the force of attraction between celestial bodies, such as planets, stars, and galaxies. The knowledge of “G” is fundamental for predicting celestial motions, designing space missions, and understanding the behavior of massive objects in the cosmos. Additionally, “G” plays a key role in various fields, including astrophysics, cosmology, and planetary science, contributing to a comprehensive understanding of the universe’s structure and evolution.


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