Plain-English Meaning
A lorry moving at 10 mph and a car moving at the same speed have different momentums — the lorry's mass makes it much harder to stop. Momentum p = mv combines mass and velocity in a single number. In any collision where no external force acts, total momentum before equals total momentum after.
Mechanics questions usually become easier once you identify whether the problem is about force balance, kinematics, energy, or conservation.
Deeper Explanation
Momentum is a vector: p = mv. Newton's second law in its most general form is F = dp/dt. Conservation of momentum follows directly when ΣF_ext = 0. In collisions: Σp_before = Σp_after; kinetic energy may be lost (inelastic) or conserved (elastic).
Worked Example
Problem: A 0.15 kg ball moving at 40 m/s is caught. What impulse stops it?
- Initial momentum p₀ = mv = 0.15 × 40 = 6 kg·m/s
- Final momentum p_f = 0 (ball at rest)
- Impulse J = Δp = p_f − p₀ = 0 − 6 = −6 N·s
Result: Impulse = 6 N·s opposing motion
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At A Glance
Category: Mechanics
Levels covered: High School, College, Masters, PhD
Best use: Start with the formula meaning, then move to the worked example and quiz so the equation turns into a tool instead of a memorised line.