Impulse/Linear Momentum

Impulse and momentum are related terms. The impulse of force can be expressed in terms of momentum.


The measure of the action of a significant force in a small interval of time is called impulse or impulsive force. Impulse is defined as the product of the average force and the time interval for which the force acts on the body. The SI unit of impulse is newton-second (N-s), and the dimensional formula of impulse is [MLT-1]. The impulse of force is equal to the change in the momentum of the body.

Linear Momentum

Newton’s second law of motion measures forces impressed on a body. For this, Newton introduced the concept of linear momentum. Linear momentum, generally called the momentum of a body, is defined as the total quantity of motion possessed by a moving body and is measured by the product of the mass and velocity of the body. Linear momentum is denoted by p. If m is the mass, and v  the velocity of a moving body, then its momentum is:

p = mv

Momentum is a vector quantity. Its direction is the direction of velocity v of the body. The SI unit of momentum is kg ms-1.

The observed effects are different when the same force is made to act on two bodies of different masses for the same time interval. The lighter body acquires a higher velocity than the heavier body. However, it is found that the change in momentum of both the bodies is the same. This leads to Newton’s second law of motion, which states that “the time rate of change of momentum of a body is directly proportional to the impressed force and takes place in the direction of the force”.

Application of Newton’s Second Law of Motion

  • Vehicles fitted with shockers

The floor of a vehicle is connected to the lower part of the vehicle by shockers or springs. When the vehicle moves over a rough road or surface, the force due to jerks is transmitted to the vehicle’s floor. The shockers increase the time of transmission of the force of jerks to the floor of the vehicle. Hence, less average force is experienced by the passengers or goods in the vehicle.

  • Glassware/chinawares wrapped in straw pieces before transportation

During transportation, the glasswares and chinawares may break if they collide with each other in the event of jerks or falls. But when these wares are wrapped in straw pieces, the force due to jerks will be transmitted to them through the pieces of straw. So, the change in momentum of the glassware takes place over a longer period of time. Therefore, a minimal average force is experienced by glasswares in the event of jerks. Hence, the chance of their breaking decreases considerably

  • Compartments of the train are provided with buffers

Buffers increase the time of impact during the shunting of the train. Thus, a small force is experienced by the compartments of the train. In other words, the compartments of the train are not damaged during the shunting of the train.

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