Impulse Calculator
Why airbags work — same impulse, longer time, smaller force.
Work out Impulse. Why airbags work — same impulse, longer time, smaller force. Written for the problem set you are stuck on.
Negative if it reverses direction.
A bat on a ball is about 1 ms. An airbag stretches it to roughly 50 ms.
Impulse
-10.5 N·s
10.5 kN average force over 1 ms
J = FΔt = Δp. The same change in momentum can be delivered as a large force briefly or a small force for longer, and the momentum change is fixed by the collision — only the force is negotiable. That is the whole principle behind airbags, crumple zones, crash mats and bending your knees on landing. None of them reduce the impulse; every one of them stretches Δt so the force comes down in proportion.
How the Impulse Calculator works
Enter mass, velocities before and after, and the contact time for the impulse and the average force. The momentum change is fixed by the collision; only the time over which it happens is negotiable.
Also known as: impulse momentum theorem calculator · change in momentum calculator · average force in a collision · impulse formula
Frequently asked questions
What is impulse?
J = FΔt, and it equals the change in momentum. Force multiplied by how long it acts gives the total effect on motion.
How do airbags reduce injury?
By stretching Δt. The momentum change in a crash is fixed by your speed and mass, so extending the stopping time from milliseconds to tens of milliseconds cuts the peak force by the same factor.
Why do you bend your knees on landing?
The same reason. Stiff legs stop you in a few centimetres; bending stretches it to half a metre, cutting the peak force by roughly ten times.
Is impulse a vector?
Yes, it has direction. A ball reversing direction has a larger momentum change than one simply stopped, which is why the sign matters in the calculation.
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