Impulse
Definition of impulse as the product of force and time, its formula (J=FΔt), and units.
What is Impulse?
The product of the average force acting on an object and the time interval over which the force acts; it is equal to the change in momentum of the object.
Key formula / rule: Impulse
Key points
- Define impulse and its relationship with force and time.
- State and apply the impulse-momentum theorem.
- Calculate impulse given force and time, or change in momentum.
- Understand the vector nature of impulse.
Common exam trap
Confusing impulse with force or momentum alone.
Definitions
- Term
Impulse
- Meaning
The product of the average force acting on an object and the time interval over which the force acts; it is equal to the change in momentum of the object.
- Term
Impulse-Momentum Theorem
- Meaning
A physics theorem stating that the impulse acting on an object is equal to the change in the object's momentum.
Learning objectives
Define impulse and its relationship with force and time.
State and apply the impulse-momentum theorem.
Calculate impulse given force and time, or change in momentum.
Understand the vector nature of impulse.
Formulae
- Name
Impulse
- Note
Favg is the average force and \Δ t is the time interval.
- Expression
J = Favg \Δ t
- Name
Impulse-Momentum Theorem
- Note
J is impulse, \Δ p is change in momentum, pf and pi are final and initial momentum, m is mass, vf and vi are final and initial velocities.
- Expression
J = \Δ p = pf - pi = mvf - mvi
Prerequisites
Force
Momentum
Velocity
Mass
Newton's Laws of Motion
Common mistakes
Confusing impulse with force or momentum alone.
Forgetting that impulse is a vector quantity and not considering direction.
Incorrectly applying the impulse-momentum theorem, especially with signs.
Using instantaneous force instead of average force in calculations.
Keywords
Impulse
Momentum
Force
Time Interval
Impulse-Momentum Theorem
Change in Momentum
Vector Quantity
Practice preview
A force of 10 N acts on a body for 5 seconds. Calculate the impulse imparted to the body.…
easy
A constant force F acts on a body of mass m for a time interval Δt. If the initial velocity of the body is u and the final velocity is v, which of the following correctly represents the impulse?…
medium
A ball of mass 0.2 kg moving with a velocity of 10 m/s collides with a wall and rebounds with a velocity of 8 m/s in the opposite direction. What is the impulse experienced by the ball?…
medium