Physics
Physics
Problem
In one or two sentences, explain why the total kinetic energy of two objects must decrease when they stick together after colliding, even though the system’s linear momentum remains unchanged.Intuitive explanation
The key insight is that momentum and kinetic energy transform differently under inelastic collisions. Momentum is conserved because no external forces act on the system, but kinetic energy depends on —so when the objects' individual velocities "average out" into a single shared velocity, the sum of squared velocities decreases, reducing total kinetic energy. The "lost" energy converts to heat, sound, and deformation rather than disappearing.
Intuitive explanation
The key insight is that momentum and kinetic energy transform differently under inelastic collisions. Momentum is conserved because no external forces act on the system, but kinetic energy depends on —so when the objects' individual velocities "average out" into a single shared velocity, the sum of squared velocities decreases, reducing total kinetic energy. The "lost" energy converts to heat, sound, and deformation rather than disappearing.