Why is the value of the Universal Gravitational Constant ($G$) so small?

The value of $G$ is indeed very small ($6.674 imes 10^{-11} N cdot m^2/kg^2$). This small magnitude is precisely why gravitational forces are only significant when dealing with extremely massive objects like planets, stars, or galaxies. For everyday objects, even those weighing several kilograms, the gravitational attraction between them is incredibly weak and practically imperceptible. If $G$ were a larger number, we would observe noticeable gravitational forces between all objects around us, which is not the case.

Does the Universal Gravitational Constant ($G$) depend on the medium between the two masses?

No, the Universal Gravitational Constant ($G$) does not depend on the medium between the two masses. Gravity is a fundamental force that acts through all media, including vacuum, air, water, or any other substance, without being absorbed, refracted, or otherwise altered. Its value remains constant regardless of what is present (or absent) between the interacting objects. This is a key aspect of its 'universal' nature.

Who first measured the value of the Universal Gravitational Constant ($G$) and how?

The value of the Universal Gravitational Constant ($G$) was first accurately measured by Henry Cavendish in 1798, using a highly sensitive apparatus known as a torsion balance. In his experiment, two small lead spheres were suspended by a thin wire. Two much larger lead spheres were then brought close to the smaller ones, causing a tiny gravitational attraction that twisted the wire. By measuring the angle of twist and knowing the properties of the wire and the masses, Cavendish was able to calculate the gravitational force and, subsequently, the value of $G$. This experiment is often referred to as 'weighing the Earth'.

What are the SI units and dimensional formula of the Universal Gravitational Constant ($G$)?

The SI units of the Universal Gravitational Constant ($G$) are Newton-meter squared per kilogram squared ($N cdot m^2/kg^2$). This can also be expressed in fundamental SI units as $m^3/(kg cdot s^2)$. The dimensional formula for $G$ is derived from these units. Since Newton ($N$) has dimensions $[M L T^{-2}]$, meter ($m$) has $[L]$, and kilogram ($kg$) has $[M]$, the dimensional formula for $G$ is $[M^{-1} L^3 T^{-2}]$. This is a frequently tested concept in competitive exams like NEET.

Gravitational Constant

Q: What is the primary difference between the Universal Gravitational Constant ($G$) and acceleration due to gravity ($g$)?

The Universal Gravitational Constant ($G$) is a fundamental constant that quantifies the strength of gravity throughout the entire universe. Its value is fixed at approximately $6.674 imes 10^{-11} N cdot m^2/kg^2$. In contrast, acceleration due to gravity ($g$) is the acceleration experienced by an object due to the gravitational pull of a specific celestial body, like Earth. Its value is not constant; it varies with altitude, latitude, and the mass and radius of the celestial body. For instance, $g$ on Earth is about $9.8 m/s^2$, but it would be different on the Moon or Mars.

Physics

NEET UG

Version 1Updated 22 Mar 2026

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The Universal Gravitational Constant, denoted by $G$ , is a fundamental physical constant that quantifies the strength of the gravitational force between two objects. It appears in Newton's Law of Universal Gravitation, which states that the gravitational force $F$ between two point masses $m_1$ and $m_2$ separated by a distance $r$ is given by $F = G \frac{m_1 m_2}{r^2}$ . This constant is universal…

Quick Summary

The Universal Gravitational Constant, denoted by $G$ , is a fundamental physical constant that quantifies the strength of the gravitational force. It is a key component of Newton's Law of Universal Gravitation, $F = G \frac{m_1 m_2}{r^2}$ , where $F$ is the gravitational force, $m_1$ and $m_2$ are the masses, and $r$ is the distance between them.

$G$ is universal, meaning its value is constant throughout the cosmos, independent of the masses, distance, or the medium between them. Its approximate value is $6.674 \times 10^{-11} N cdot m^2/kg^2$ .

This extremely small value explains why gravitational forces are only significant for very massive objects. The SI units of $G$ are $N cdot m^2/kg^2$ or $m^3/(kg cdot s^2)$ , and its dimensional formula is $[M^{-1} L^3 T^{-2}]$ .

Henry Cavendish first measured $G$ using a torsion balance. It is crucial not to confuse $G$ with $g$ , the acceleration due to gravity, which is a variable quantity dependent on the celestial body and location.

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Key Concepts

Distinction between G and g

It's vital to differentiate between the Universal Gravitational Constant ( $G$ ) and the acceleration due to…

Significance of G's Small Value

The extremely small magnitude of $G$ ( $6.674 \times 10^{-11} N cdot m^2/kg^2$ ) has profound implications. It…

Units and Dimensional Analysis of G

Understanding the units and dimensional formula of $G$ is crucial for NEET. From Newton's Law, $F = G…

Definition: — Universal Gravitational Constant,

G

Formula: —

F = G \frac{m_1 m_2}{r^2}

Value: —

G approx 6.674 \times 10^{-11} N cdot m^2/kg^2

Units: —

N cdot m^2/kg^2

m^3/(kg cdot s^2)

Dimensions: —

[M^{-1} L^3 T^{-2}]

Nature: — Universal, scalar, independent of mass, distance, medium.

Discovery: — First measured by Henry Cavendish (1798) using a torsion balance.

Key Distinction: — Not to be confused with

g

(acceleration due to gravity), which is variable.

Great Men Love To Derive Units: Gravitational constant, Mass (inverse), Length (cubed), Time (inverse squared), Dimensions, Units.