1. What Is Momentum?
Momentum tells us how much ‘motion’ an object has. It depends on two things: how heavy the object is and how fast it is moving.
In simple terms, momentum is the quantity of motion an object possesses.
1.1. Definition of Momentum
Momentum is defined as the product of an object's mass and velocity:
\( p = mv \)
where:
- \( p \) = momentum
- \( m \) = mass of the object
- \( v \) = velocity
1.2. Why Momentum Matters
Momentum helps explain why heavier or faster-moving objects are harder to stop. A fast-moving cricket ball hurts more than a slow one because it has more momentum.
2. Properties of Momentum
Momentum has some important characteristics that help describe motion in physics.
2.1. Momentum Is a Vector Quantity
Momentum has both magnitude and direction because it depends on velocity, which is a vector. This means the direction of momentum is the same as the direction of motion.
2.2. Unit of Momentum
The SI unit of momentum is:
\( \text{kg·m/s} \)
3. Momentum in Real Life
Momentum plays a key role in many simple everyday activities.
3.1. Examples
- A truck moving slowly can have more momentum than a bicycle moving fast, because the truck has a much larger mass.
- Catching a fast cricket ball is difficult because it has large momentum.
- A rolling bowling ball knocks down pins due to its high momentum.
4. Changing Momentum
Momentum changes when either mass or velocity changes. Since mass is usually constant, momentum usually changes when velocity changes.
4.1. Force and Rate of Change of Momentum
Newton’s second law can be written in terms of momentum:
\( F = \dfrac{\Delta p}{\Delta t} \)
This shows that force is needed to change momentum.
4.2. Examples of Changing Momentum
- A goalkeeper moves hands backward while catching a football to reduce force by increasing stopping time.
- When a bat hits a cricket ball, it quickly changes the ball’s momentum.
5. Zero Momentum
If an object is at rest, its velocity is zero. So its momentum is also zero:
\( p = mv = m \times 0 = 0 \)
5.1. Examples
- A book lying on a table has zero momentum.
- A stationary car has zero momentum, even if it is very heavy.