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Impulse
Beginner
Change in momentum caused by a force acting over time.
J = FΔtImpulse J = ∫F dt measures a force's effect over time and equals the change in momentum. The same impulse can come from a big force briefly or a small force for longer.
A 1500 N kick lasting 0.02 s gives J = 30 N·s.
Impulse is a vector; use signs.
In more detail
Impulse is the product of the average force and the time over which it acts, and it equals the change in momentum. It is measured in newton seconds.
Real-world uses
- Increasing the time of contact in a jump reduces the average force on the legs.
- Racket sports rely on impulse to change the ball's direction and speed.
- A golf club gives the ball an impulse during the short time of contact, changing its momentum from zero to a large value.
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Frequently asked questions
Does a large impulse need a large force?
Not necessarily. A small force acting for a long time can give the same impulse as a large force for a short time.
What is the unit of impulse?
Newton seconds, equal to kilogram metres per second.
How do I calculate impulse from a graph?
Find the area under the force-time graph, which equals the impulse and therefore the change in momentum.
Related topics in Momentum & Collisions
Linear momentum · Momentum is a vector · Impulse–momentum theorem · Why airbags work · Conservation of momentum