Momentum and Impulse
Conservation of linear momentum and impulse–momentum theorem. (Physics › Laws of Motion, NEET UG syllabus.)
What is Momentum and Impulse?
The product of an object's mass and its velocity. It is a vector quantity that describes the 'quantity of motion'.
Key formula / rule: Linear Momentum
Key points
- Define momentum and impulse and state their SI units.
- Calculate momentum for objects in motion.
- Apply the principle of conservation of linear momentum to solve problems involving collisions and explosions.
- Relate impulse to the change in momentum using the impulse-momentum theorem.
Common exam trap
Confusing momentum with kinetic energy (momentum is vector, KE is scalar).
Definitions
- Term
Momentum
- Meaning
The product of an object's mass and its velocity. It is a vector quantity that describes the 'quantity of motion'.
- Term
Impulse
- Meaning
The change in an object's linear momentum. It is also defined as the product of the average force acting on an object and the time interval over which the force acts.
- Term
Isolated System
- Meaning
A system of particles on which no net external force acts. Internal forces between particles within the system do not affect the total momentum of the system.
Learning objectives
Define momentum and impulse and state their SI units.
Calculate momentum for objects in motion.
Apply the principle of conservation of linear momentum to solve problems involving collisions and explosions.
Relate impulse to the change in momentum using the impulse-momentum theorem.
Solve problems involving average force, time of impact, and change in momentum.
Explain real-world applications of momentum and impulse concepts.
Formulae
- Name
Linear Momentum
- Note
p is momentum, m is mass, v is velocity. p is a vector quantity.
- Expression
p = mv
- Name
Impulse
- Note
J is impulse, Favg is average force, Δt is time interval. J is a vector quantity.
- Expression
J = Favg × Δt
- Name
Impulse-Momentum Theorem
- Note
Impulse equals the change in linear momentum.
- Expression
J = Δp = pfinal - pinitial
- Name
Conservation of Linear Momentum
- Note
For two bodies: m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂ (vector sum).
- Expression
Σpinitial = Σpfinal (for an isolated system)
Prerequisites
Newton's Laws of Motion (especially the Second and Third Laws)
Basic understanding of vectors (addition, subtraction, direction)
Concepts of mass, velocity, and acceleration
Kinematics of one and two dimensions
Common mistakes
Confusing momentum with kinetic energy (momentum is vector, KE is scalar).
Forgetting the vector nature of momentum and impulse (direction matters).
Applying conservation of momentum when external forces are present.
Incorrectly calculating change in momentum (always final minus initial).
Not understanding that N·s and kg·m/s are equivalent units for impulse/momentum.
Keywords
Momentum
Impulse
Conservation of Momentum
Impulse-Momentum Theorem
Collision
Recoil
Isolated System
Vector
Practice preview
What is the SI unit of linear momentum?…
easy
Impulse is defined as the product of:…
easy
A ball of mass 0.5 kg moving at 10 m/s strikes a wall and rebounds with a speed of 8 m/s in the opposite direction. What is the magnitude of the impulse imparted to the ball by the wall?…
medium