← ⚛️ Physics · usually met in Std 9-12
Mass times velocity — how hard something is to stop. In any collision the total stays the same, which makes it one of physics' most useful bookkeeping rules.
A loaded lorry at walking pace and a cricket ball at speed can carry similar momentum, and both are harder to stop than they look. In a closed system the total momentum before a collision equals the total after, whether the objects bounce apart or stick together. That conservation is what lets you work out the result of a collision without knowing anything about the forces during it.
It also explains safety design. A crumple zone does not reduce the change in momentum in a crash — that is fixed by the speed and the mass. It stretches the change over more time, and since force is the rate at which momentum changes, more time means less force on the people inside. An airbag, a helmet's lining and a cricketer's gloves all do the same arithmetic.
Want to see it moving? Search YouTube for “Momentum” ↗ — we send you to the search rather than to one video, because a link to one video eventually rots.
This entry was written for Star Student in our own words — it is a summary, not a source. Here is where the people who actually hold these facts keep them. Go and check.
Your own textbook ↗Balbharati publishes the textbooks free to read online. Your chapter is the thing to check first — an encyclopedia is a summary, and the syllabus is the syllabus.Last gone through: 1 October 2026 · How these entries are written
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