Impulse Calculator: J = Ft

The impulse of a force acting for a short time.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

Choose which quantity you want to find.

Enter the other values in the units shown.

The calculator gives the answer with the formula, the substituted numbers, and the answer in other units.

Formulas used

  • J = F\,t
  • F = \frac{J}{t}
  • t = \frac{J}{F}

Worked example

With the default numbers in the calculator above:

  1. The formula, arranged to find the impulse: impulse = average force x contact time
  2. Put the values in (every value in its SI unit): impulse = 500 x 0.02
  3. The answer: impulse: 10 N s
  4. The same answer in other units: 10 kg m/s; 2.24809 lbf s

Change the numbers in the calculator to see the full working, every step, for your own case.

Common questions

What is impulse?

The force times the time it acts, which equals the change in momentum of the object.

Why does a longer stopping time reduce the force?

For the same change in momentum, the force is the impulse divided by the time, so more time means less force.

What is the unit of impulse?

The newton second, the same as kg m/s.

Related calculators

Got a question about this? Ask an engineering question and get a plain-language answer with references.

Further reading: Any school physics text (impulse and momentum).

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