The term Momentum is commonly used in sports. When a commentator says that a player has the momentum, it means that the player is actually on the move and very difficult to stop. Momentum is a concept of physics. Any body that has a momentum is difficult to stop and it is mandatory to apply a force against its direction of motion for a particular period of time. More the momentums a body has, the harder it is to stop. Hence, a higher amount of force is required or a considerable time period to bring the body to a halt. As the force acts on the body for a given time, the body’s velocity changes and hence the body’s momentum changes.

A force changes the velocity of an object in either way. Also, if the object’s velocity changes, the momentum also changes.

What is Impulse?

According to Newton’s second law, i.e, Fnet = m. An acceleration of a body is directly proportional to the net force that acts on the body and inversely proportional to the mass. If combined with the acceleration (a = ?v / t), the resultant equation is described as:

F = m • a


F = m • ?v / t

When both sides of the equation are multiplied by t, a new equation formed is expressed as:

F • t = m • ?v

The above equation describes one among the two primary principles to be applied in the analysis of collision. According to texts in books of Physics, Impulse is defined as the change in momentum, calculated by multiplying force with time. Since momentum is mass multiplied by velocity, the quantity m•?v equals to change in momentum.

You need to understand the physics behind collisions. The collisions are based on the laws of momentum and the first law is described in the above equation, known as the change in impulse equation.

The body experiences a force in a collision for a particular period of time and results in the change of momentum. The impact of the force acting for a particular amount of time is that the body either slows down or speeds up or changes its direction.

The object experiences an impulse in a collision and this impulse equals to the change in momentum. For instance, a football halfback who is running down the field and encounters a collision by a defensive back. The collision changes the halfback’s speed and therefore his momentum.

Impulse Application

A cricket player lowers his hand just before catching the ball. This increases the time of impact and decreases the effect of force.

When someone falls from the bed on a floor receives more injuries when compared to falling on a heap of sand. This happens because of the sand yields more than the cemented floor, therefore, increasing the impact time and lowers the impact of force.

Practise This Question

A Man moves on a straight horizontal road with a block of 2kg in his hand. If he covers a distance of 20m with constant velocity of 1m/s. Find work done by man on block during motion.