Impulse Calculator (J = Ft)

This impulse calculator uses J equals Ft, where impulse is force multiplied by the time it acts. Choose the unknown and enter the others; the calculator solves for impulse, force or time. Impulse measures the overall effect of a force over a period, and it equals the change in an object\u2019s momentum, which is why a longer contact time means a gentler force for the same momentum change, the idea behind crumple zones and follow-through in sport. Impulse is measured in newton seconds, the same as momentum in kilogram metres per second. The formula, a worked example and the assumptions are below.

Impulse (N\u00B7s)

Force (N)

Time (s)

Solve for

Value

Result

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

Related calculators

Kinetic Energy Calculator: energy of motion.
Momentum Calculator: mass times velocity.
Projectile Motion Calculator: range and height.

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