Impulse
Impulse is force over time and equals the change in momentum.
About this topic
Impulse is the force multiplied by the time over which it acts, J = FΔt, and it equals the change in momentum, Δp. The area under a force-time graph is the impulse.
Increasing the stopping time reduces the average force for the same momentum change, so airbags, crumple zones, padded gloves and bending your knees on landing all protect the body. Conversely, a short, hard hit gives a big force, as with a hammer. A follow-through in golf or tennis lengthens contact time and raises the impulse.
Example: a 0.15 kg cricket ball moving at 30 m/s is caught and stopped in 0.01 s by bare hands, with a force of 450 N; letting the hands move back for 0.1 s cuts it to 45 N. A 70 kg person landing at 5 m/s stopping in 0.5 s experiences 700 N, but in 0.05 s it is 7000 N. Helmets, seat belts, trampolines and gymnastic mats use the same principle.
Common misconception: airbags do not reduce the momentum change, which is fixed; they reduce the force by increasing the time. Remember that impulse is a vector, and uses the net force.
Key ideas
- J = FΔt = Δp
- Airbags lengthen the time to reduce force
- Area under an F–t graph
Quick check
Use cases: where Impulse helps
- Homework: review the key idea behind Impulse before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Impulse without notes.
- Visual learning: play with the interactive lab to see how Impulse changes when you adjust its inputs.
- Teaching a friend: explain Impulse in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Impulse?
Impulse is force over time and equals the change in momentum.
What will I learn in Impulse?
J = FΔt = Δp. Airbags lengthen the time to reduce force. Area under an F–t graph.
Is Impulse part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Impulse lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Impulse?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.