“Every particle in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.”
Mathematically, the law is represented as:
F = (G m1m2) / r2
Where:
F is the gravitational force between two objects,
G is the gravitational constant (approximately 6.67430 × 10-11 N m2 / kg2),
m1 and m2 are the masses of the two objects, and
r is the distance between the centers of the two objects.
The law of gravitation explains how objects with mass attract each other and is responsible for the force that keeps celestial bodies like planets, moons, and stars in their orbits.
Proportional to the product of masses: The gravitational force between two objects is directly proportional to the product of their masses. This means that if either of the masses increases, the force of attraction between them will also increase.
Inversely proportional to the square of distance: The gravitational force is inversely proportional to the square of the distance between the centers of the two objects. As the distance increases, the force of attraction decreases rapidly. If the distance is doubled, the force becomes one-fourth of its original value, and if the distance is halved, the force becomes four times its original value.
The important thing to remember is that the force you apply on an object is equal to the force that object will apply back on you
Hence, Newton law of gravitation is consistent with Newton’s third law of motion.
A gravitational field is a region around an object, where other objects experience a force of attraction towards the object. The strength of the gravitational field is proportional to the mass of the object and decreases with distance. The gravitational field does not need a medium to attract an object towards itself, so it works in space too.
“Gravitational field strength “g” is the gravitational force acting per unit mass.”
The “g” (acceleration due to gravity) is the acceleration that an object experiences when it falls freely under the influence of gravity.
When an object is in free fall, it falls vertically downwards under the influence of gravity and experiences a constant acceleration of g.
When an object is thrown upwards, the gravity acting on it constantly decreases.
The value of g is 9.8 m/s2 on the surface of the Earth. This means an object dropped from rest will fall 9.8 metres in the first second of its motion. On the other hand, when an object is thrown upwards, the acceleration of gravity decreases constantly.
When an object is in free fall, it experiences no air resistance, which means that the only force acting on it is gravity.
Example:
Any object falling on the Earth experiences a pull of 9.8 Nkg-1 like an apple falling from a tree.
The gravitational pull an object experiences varies from planet to planet.
| Planet | Acceleration of Gravity "g" (m/s2) |
|---|---|
| Earth | 9.8 |
| Moon | 1.62 |
| Venus | 8.87 |
| Mars | 3.77 |
| Jupiter | 25.95 |
| Sun | 274 |
| Mercury | 3.59 |
| Saturn | 11.08 |
| Uranus | 10.67 |
| Neptune | 14.07 |
Remember that the lowercase “g” and capital “G” are separate, even if they seem identical. The lowercase “g” is the constant of the gravitational field and is usually used to represent the gravity of Earth. The uppercase “G” is the constant of gravity between two bodies.
| Gravitational Constant “G” | Acceleration of Gravity “g” |
|---|---|
| The gravitational constant “G” is a numerical value that determines the strength of the gravitational force between two objects. | “g” is the acceleration due to gravity, it represents the rate at which objects fall towards the ground when dropped. |
| The unit of “G” is Nm2/kg2. | The unit of “g” is m/s2. |
| The purpose of “G” is to calculate the force of attraction between two objects due to gravity. | The purpose of “g” is to calculate the acceleration of an object that is falling freely under the influence of gravity. |
| “G” is a constant that does not change with location and altitude. | “g” changes with location and altitude. |
“The weight of an object is the measurement of gravitational force acting on the object.”
Definition:
Weight is the force with which a body is attracted towards the centre of the earth by the earth’s gravitational field.
Formula:
Weight is given by the formula
W=mg
Where W is the weight, m is the mass of the object, and g is the acceleration due to gravity. Weight is commonly measured in Newtons (N) or kilograms (kg).
Example:
The weight of an apple is 100 g or 1 N.