# Momentum and Gravity

Momentum is a word that is commonly used in everyday life. When a person says that a sports team has a lot of momentum, it implies that the team has had a lot of recent success. It has almost the same meaning in physics, though in physics, it needs to be more specific.

## Momentum

The measurement of the mass in motion is called momentum. Linear momentum, also known as momentum, is measured as the product of mass and velocity. Momentum is a vector quantity denoted by the letter p. The unit of momentum is kg.m/s.

By definition p = m.v

Where m is the mass and v is the velocity

The above relationship means that doubling the mass or velocity of the object will double the momentum. The equation of momentum can also be written in terms of force. From the kinetic equations, the change in velocity △v can also be written as a. △t.

The change in momentum following an acceleration is given as:

△p = m.△v

△p = m. a.△t

= F.△t

## Impulse-Momentum Theorem

Sometimes a very large force acts for a very short interval of time and produces a finite change in the momentum of the body. In such a case, neither the force nor the time interval for which the force acts can be measured.  However, the effect produced by force, i.e., change in momentum, can be measured. Impulse is expressed by the symbol J and is measured in newton – seconds.

For a constant force, J = F.△t

The above expression is the equivalent to the expression for the change in momentum, △p.

This equivalence is known as the impulse-momentum theorem.

## Law of Conservation of Momentum

Conservation of momentum is a consequence of Newton’s second and third laws of motion. The law of conservation of momentum, which can be deduced from Newton’s second and third laws of motion, is an important law in mechanics. The law is especially useful for analysing problems that deal with the collision between particles. The law states that the recoil of the gun is an example of the law of conservation of momentum.

## Gravity

Science has explained gravity as the attractive force between all the objects in the universe. The concept of gravity can be explained by the universal law of gravitation. According to the universal law of gravitation, every object will attract every other object with force directly proportional to the product of their masses and inversely proportional to the square of the separation between them.

F = Gm1m2/d2

m1 and m2 are the masses of the two objects

d is the distance between the two objects

G is the gravitational constant = 6.673 x 10-11 Nm 2 Kg-2

## Does Gravity Violate the Conservation of Momentum?

The law of conservation of momentum does not apply when there is an external force.  If the object and Earth are considered a closed system, then there is no external force. In the closed system, when an object moves downwards due to gravitational force, its downward momentum is balanced by the upward momentum due to Earth. Therefore, momentum is conserved with gravity.