When you throw a ball, it naturally goes up only till a height and then falls down, same is true for anybody, it is pulled down by earth, there is an unseen magnetic force that attracts all objects towards itself constantly. Have you ever wondered what this pull could be?

This force of attraction is known as gravitation or gravitation pull.

Universal Law of Gravitation

Every object in the universe attracts another object by a force of attraction, called gravitation, which is directly proportional to the product of masses of the objects and inversely proportional to the square of the distance between them. This is called Law of Gravitation or Universal Law of Gravitation.

This attractive force exists between any two objects varies based on mass, Larger objects always exert this force on smaller objects. In a similar way, the moon is orbiting around earth due to the gravitational force of the earth. Planets are orbiting around sun due to the gravitational force of the sun. According to Newton's law of gravitation, The gravitational force is directly proportional to the product of the two masses and inversely proportional to the square of the distance between them.


F= Gravitational force between two objects
m1 = Mass of object 1
m2 = Mass of object 2
d = Distance separating the objects centers

G = gravitational constant

Gravitational force was discovered by Sir Isaac Newton in 1687. Gravitational force is the weakest force among the four fundamental forces of nature.

Free Fall

When an object falls from any height under the influence of gravitational force only, it is known as free fall. In the case of free fall, no change of direction takes place but the magnitude of velocity changes because of acceleration.

This acceleration acts because of the force of gravitation and is denoted by ‘g’. This is called acceleration due to gravity.


Mass is the measurement of inertia.

Inertia is the property of any object which opposes the change in state of the object. It is because of inertia than an object in rest has a tendency to remain at rest and an object in motion has a tendency to remain in motion.

Inertia depends upon the mass of an object. An object having greater mass has greater inertia and vice versa. Mass of an object remains constant everywhere, i.e. mass will remain same whether that object is at the moon, at the earth or anywhere in the universe.

Thrust and Pressure

Thrust: Force exerted by an object perpendicular to the surface is called thrust.

Pressure: Force exerted by any object per unit area is called pressure.

∴Pressure=Force x Area

Or, Pressure=Thrust x Area

Or, p=FA ---(i)

Where, p is pressure, F is thrust or force and A is the surface area of the object.

Since pressure is indirectly proportional to the surface area of the object, thus, pressure increases with decrease in surface area and decreases with increase in surface area.


Buoyancy is the upward force exerted by fluids over the surface area of contact with an object which is immersed in fluids. Buoyancy is also known as upward thrust.

When an object is immersed in water, it exerts pressure over water due to its weight. At the same time water also exerts upward thrust over the object. If the force exerted by the object is greater than the upward thrust or buoyancy by water, the object sinks in water otherwise it floats over water.

This is why does an object sinks or floats over water!