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Impulse
Intermediate
Force integrated over time, equal to change in momentum.
J = ∫F dt = ΔpImpulse is the force integrated over time and equals the change in momentum: J = ∫F dt = Δp. For constant force J = FΔt. The area under an F–t graph gives it.
A 0.15 kg ball hit from +20 to −30 m/s: Δp = 7.5 N·s.
Direction matters: reversing direction doubles the change.
In more detail
Impulse is the product of force and the time it acts, and it equals the change in momentum. A large force for a short time can produce the same impulse as a small force for a longer time.
Real-world uses
- Airbags increase the time of impact, reducing the peak force on passengers.
- Golfers and tennis players follow through to increase the time the racket is in contact with the ball.
- A tennis player follows through a serve to make the impulse larger over a longer contact time, reducing the peak force on the ball.
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Frequently asked questions
What are the units of impulse?
Newton seconds, which are equal to kilogram metres per second.
Is impulse the same as momentum?
No. Impulse is a change in momentum, not momentum itself.
Why do airbags reduce injuries?
They increase the time over which a passenger slows down, so the force for the same change in momentum is much smaller.
Related topics in Newton's Laws & Forces
Rolling friction · Friction on inclines with applied force · Block on block problems · Linear momentum · Second law as rate of momentum change · Variable mass systems