How to calculate impulse from force and time
Impulse measures the effect of a force acting over time. A smaller force acting for longer can give the same momentum change as a larger force acting briefly.
What the formula is saying
For constant force, impulse J = FΔt. For a varying force, F must be the time-average over the interval. Impulse equals change in momentum when F is the net force.
Read the symbols in plain language
- F
- ForceN
- Δt
- Time intervals
Sort out the units first
Use N and seconds for N·s. 200 milliseconds = 0.2 s. N·s is not the same as N/s.
Let’s solve one together
Read the given values, follow each operation, then check what the result means.
- F · Force
- 100 N
- Δt · Time interval
- 0.2 s
Convert the duration to seconds
Use the interval for which the stated force acts.
(0.2) = 0.2 sMultiply force by duration
This is the area under a constant-force versus time graph.
(100) × (0.2) = 20 N·s
Does this worked answer make sense?
The example gives 20 N·s, equivalent to 20 kg·m/s of momentum change when F is the net force.
Now try your own values
Change a value or its unit. The same method will show your calculation, step by step.
Results update only when you calculate. The lesson example above stays unchanged.
Your turn — check your understanding
Use these new values. Work it out first, then check your answer.
- F · Force
- 60 N
- Δt · Time interval
- 0.5 s
Find: impulse from force and time
A hint, not the answer
For constant force, impulse J = FΔt. For a varying force, F must be the time-average over the interval. Impulse equals change in momentum when F is the net force.
Use N and seconds for N·s. 200 milliseconds = 0.2 s. N·s is not the same as N/s.
Show the full practice solution
Compare the steps with your work; revealing a solution does not mark the lesson complete.
Convert the duration to seconds
Use the interval for which the stated force acts.
(0.5) = 0.5 sMultiply force by duration
This is the area under a constant-force versus time graph.
(60) × (0.5) = 30 N·s
Avoid the common trap
Do not use the peak of a changing force as its average without justification. The duration is a time interval, not a clock timestamp.
When this method applies — and when it does not
Constant force or a correctly determined time-average. For nonconstant forces without an average, integrate force over time.
For study and understanding, not approval of a real structure, site operation or design. Apply the correct standard, National Annex and professional review to actual engineering work.
One idea understood. Keep going.
This optional checkmark is saved only in this browser. It is your own progress note, not a certificate.
Sources & further reading
References open in a new tab and explain the underlying principles. The teaching text and examples here are SimpleFlick’s own; the source organisations have not endorsed this calculator.
Lesson updated: · Worked examples checked against the implemented formula; not an independent engineering certification.