An object that falls under the sole influence of gravity is known as a free-falling object. A free-falling object has an acceleration of 9.8 m/s2, downward (on Earth). This numerical value is so significant that it is given a special name as the acceleration of gravity. We denote it with the symbol g.
The force of attraction between any two unit masses separated by a unit distance is called the universal gravitational constant. The universal gravitational constant is denoted by the symbol G and is measured in Nm2/kg2. The numerical value of G is 6.67 × 10-11 Nm²/Kg².
The relation between G and g is not proportional. This means that they are independent entities.
Relationship Between G and g
In physics, G and g related to each other as follows:
| g=GM/R2 |
Where,
- g is the acceleration due to the gravity measured in m/s2.
- G is the universal gravitational constant measured in Nm2/kg2.
- R is the radius of the massive body measured in km.
- M is the mass of the massive body measured in Kg
Although there exists a formula to express the relation between g and G in physics, there is no correlation between acceleration due to gravity and universal gravitation constant, as the value of G is constant. The value of G is constant at any point in this universe, and G and g are not dependent on each other.
What is G and g?
The G and g are distinct entities in physics. Below is the table of the difference between G and g.
| Symbol | Definition | Nature of Value | Unit | |
| Acceleration due to gravity | g | The acceleration experienced by a body under free fall due to the gravitational force of the massive body | Changes from place to place.Acceleration due to gravity of the earth is 9.8 m/s2 | m/s2 |
| Universal Gravitational Constant | G | The force of attraction between two objects with unit mass separated by a unit distance at any part of this universe. | Constant at any point in this universe.G = 6.67×10-11 Nm2/kg2 | Nm2/kg |
Deriving the relationship between g and G
According to the universal law of gravitation,
F = G M m R 2 ————(1)
From Newton’s second law of motion, we know that
F = m a ———–(2)
If the acceleration due to gravity is g at a given point, then the above equation becomes
F = m g ———–(3)
Substituting equation (3) in (1), we get-
m g = G M m R 2
Simplifying the above equation, we get
g = G M R 2
Thus, we arrive at the relationship between g and G as –
⇒ g = G M R 2