Momentum and Collisions; Jet Propulsion
One conserved quantity that solves crashes, recoil and rockets in a single line of arithmetic
Big Idea: Every moving body carries a quantity called momentum, p = mv. When bodies push on each other — two cars colliding, a rifle firing a bullet, a rocket firing its engine — the total momentum of the whole group does not change, provided no outside force acts. This single rule, the law of conservation of momentum, lets you predict a final velocity even when the forces during the interaction are far too complicated to measure. In grades 7–9 you solved motion with forces and energy; here you add the third great bookkeeping tool of mechanics.
By the end you will be able to:
- define momentum as a vector and give its SI unit;
- use the impulse–momentum theorem FΔt = Δp;
- state when momentum is conserved and apply Σpbefore = Σpafter;
- tell elastic from inelastic collisions and know what survives each;
- explain jet (reaction) propulsion and recoil using momentum;
- solve multi-step numeric problems with correct signs and units.