Impulse Calculator (J = Ft)

This impulse calculator solves J = Ft, working out impulse, force or time whenever you know the other two values. Impulse is the effect a force has when it acts over a period, and it equals the change in an object's momentum, which is why the same change in speed can come from a small force acting for a long time or a large force briefly. Pick the quantity you want using the "Solve for" menu, then enter the two known values: impulse in newton seconds, force in newtons and time in seconds. The calculator instantly returns the missing value in the results card, showing the main answer alongside a value and result summary so you can see what has been solved. It rearranges the relationship, using F = J / t and t = J / F, so you can move between the three variables without redoing the algebra. A worked example shows a 5 newton force acting for 4 seconds producing an impulse of 20 newton seconds, reproducible by entering those figures. Use it for physics homework, classroom demonstrations, or quick checks involving collisions and braking, where a longer contact time lowers peak force for the same momentum change, the idea behind airbags and crumple zones. It assumes a constant force and correct SI units, so treat results as an indicative estimate, not a substitute for full working.

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Impulse (N·s)

Force (N)

Time (s)

Solve for

Impulse = 20 N·s

Value20

Resultsolved for Impulse

The formula

Impulse is J = Ft, force times the time it acts, for a constant force. It equals the change in momentum, J = m times the change in v. Rearranged: F = J / t and t = J / F.

Worked example

A constant force of 5 N acting for 4 seconds delivers an impulse of J = 5 times 4 = 20 newton seconds, changing the momentum by 20 kg m/s. Solve for J with F = 5, t = 4 to confirm.

Frequently asked questions

What is impulse?

The product of a force and the time it acts. It equals the change in momentum it causes.

What units is impulse in?

Newton seconds, which are the same as kilogram metres per second, the units of momentum.

Why does contact time matter?

For the same momentum change, a longer time means a smaller force, which is how airbags and crumple zones reduce injury.

Who this calculator is for

This calculator is for physics students, teachers and engineers.

What this calculator assumes

You enter SI units as labelled.
One variable is solved from the others.
Results are rounded for display.

Formula and sources

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