Momentum and Conservation of Momentum
Momentum p = mv. In an isolated system, total momentum is conserved. This principle is used to analyse collisions and explosions.
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Momentum
The linear momentum of an object is the product of its mass and velocity: p = mv. It is a vector (same direction as velocity). The SI unit is kg·m/s. A fast-moving object or a heavy object can have large momentum. Momentum is central to understanding collisions and the effect of forces over time (impulse).
Conservation of momentum
When no net external force acts on a system, the total momentum of the system remains constant. This is the law of conservation of momentum. It holds for collisions (elastic or inelastic), explosions, and any interaction within an isolated system. For two bodies: m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂ (before and after).
Applications
Conservation of momentum is used to find velocities after collision when forces during the collision are not known. Rocket propulsion can be explained by momentum: the rocket pushes exhaust backward, and by Newton's third law and conservation of momentum, the rocket moves forward.
In a head-on collision of two cars, how does the total momentum before the crash compare to the total momentum after? What about the total kinetic energy?