Impulse of Force

Introduction

In many situations, a force acts on a body for a short time and produces a noticeable change in motion. This effect of force acting over a time interval is called impulse.

Impulse of Force

Impulse is defined as the product of force and the time for which it acts.

Impulse = Force × Time

J = F × t

Impulse is also equal to the change in momentum of a body.

Impulse = Change in Momentum

Explanation

When a force acts on a body for a certain time, it changes the momentum of the body. A large force acting for a short time can produce the same effect as a small force acting for a longer time.

• If time of contact increases, force decreases for the same change in momentum.
• If time of contact decreases, force increases.

This is why we try to increase the time of impact to reduce force in many real-life situations.

Examples from Daily Life

• A cricketer moves his hands backward while catching a ball to increase time and reduce force.
• Airbags in cars increase the time of collision and reduce injury.
• A person bends knees while jumping from a height to reduce the force of impact.
• Hammering a nail involves applying a large force for a short time.

Illustration

When the ball hits a hard surface, the time of contact is very small, so the force is large. On a soft surface, the time of contact increases, so the force decreases. This shows the concept of impulse.

Important Points

• Impulse = Force × Time.
• Impulse is equal to change in momentum.
• Increasing time of contact reduces force.
• Decreasing time of contact increases force.
• Unit of impulse is newton-second (N·s).

Conclusion

Impulse of force explains how force acting over time changes the momentum of a body. It helps us understand many safety techniques and real-life situations involving collisions.