1. What Is Impulse?
Impulse tells us how much the momentum of an object changes when a force acts on it for a short time. It combines two things:
- How strong the force is
- How long the force acts
In simple terms: Impulse = Force × Time.
1.1. Impulse in Everyday Life
Many real-life actions involve force applied for a short time — like hitting a ball with a bat, catching a cricket ball, or a hammer striking a nail. These are examples of impulse.
2. Mathematical Definition of Impulse
Impulse is given by the formula:
\( J = F \Delta t \)
where:
- \( J \) = impulse
- \( F \) = constant force
- \( \Delta t \) = time duration of the force
2.1. Units of Impulse
The SI unit of impulse is the same as momentum:
\( \text{kg·m/s} \)
2.2. Impulse When Force Is Not Constant
If force changes during the interaction (such as when hitting a ball), impulse is the area under the force–time graph.
3. Impulse and Change in Momentum
Impulse is closely related to momentum. When a force acts on an object for some time, it changes the object’s momentum.
The relation is:
\( J = \Delta p = m v_2 - m v_1 \)
This means impulse equals the change in momentum.
3.1. Why This Relation Matters
The greater the impulse, the greater the change in momentum. This idea explains many everyday actions like catching, hitting, pressing brakes, or throwing objects.
4. Examples of Impulse in Daily Life
Impulse helps us understand safety equipment, sports techniques, and everyday actions.
4.1. Catching a Ball
A cricketer moves hands backward while catching a fast ball. This increases stopping time, reducing the force and making the catch easier.
4.2. Airbags in Cars
Airbags increase the stopping time during a collision. This reduces the force acting on passengers, even though momentum change is the same.
4.3. Hammer and Nail
A hammer strikes the nail with a large force in a very short time — a strong impulse pushes the nail into the wood.
4.4. Kicking a Football
When a footballer kicks the ball, force applied over a short time gives a large impulse, increasing the ball’s momentum quickly.
5. Impulse in Collisions
Impulse is especially important during collisions because forces act for very short durations but can be very large.
5.1. Soft vs Hard Surfaces
When an object hits a soft surface (like a cushion), the stopping time increases, reducing the force. Hard surfaces reduce stopping time, increasing force.
5.2. Example
A glass dropped on a soft carpet may not break because the stopping time is longer and the force is smaller. On a hard floor, stopping time is tiny, so force is large — the glass breaks.