Momentum and Impulse
Momentum is the product of mass and velocity. The law of conservation of momentum states that in a closed system the total momentum before a collision equals the total momentum after.
What You Need to Know
Key Concept Diagram
Momentum p = mv (kg·m/s), where m is mass (kg) and v is velocity (m/s)
Impulse = force × time = change in momentum (FΔt = mΔv)
Law of conservation of momentum: total momentum before collision = total momentum after in an isolated system
Elastic collisions conserve both momentum and kinetic energy; inelastic collisions conserve only momentum
Key Vocabulary
Momentum
The product of an object's mass and velocity (p = mv); a vector quantity measured in kg·m/s
Impulse
The product of force and the time over which it acts; equals the change in momentum of an object
Conservation of momentum
The principle that the total momentum of an isolated system remains constant when no external forces act
Elastic collision
A collision in which both momentum and kinetic energy are conserved
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
A 2 kg ball moves at 5 m/s. What is its momentum?
Question 2
In a closed system, a 3 kg cart moving at 4 m/s collides with a stationary 1 kg cart. They stick together. What is their combined velocity?
Question 3
What does impulse equal in terms of momentum?
Key Concepts Summary
- ●Momentum p = mv (kg·m/s), where m is mass (kg) and v is velocity (m/s)
- ●Impulse = force × time = change in momentum (FΔt = mΔv)
- ●Law of conservation of momentum: total momentum before collision = total momentum after in an isolated system
- ●Elastic collisions conserve both momentum and kinetic energy; inelastic collisions conserve only momentum