Savchenko Problem 2.5.2
Physics · thermodynamics
Problem
A ball of the same mass strikes a stationary ball. Find the angle of flight of the balls after an off-center elastic impact.Intuitive explanation
When two identical balls collide elastically off-center, momentum and kinetic energy are both conserved—but the collision isn't head-on, so forces act perpendicular to the line joining their centers. The key insight is that the component of velocity along the line of centers gets exchanged (like a head-on collision), while the perpendicular components remain unchanged. This means you'll find two scattering angles by decomposing velocities into radial and tangential parts, then using the geometry of the impact.
Intuitive explanation
When two identical balls collide elastically off-center, momentum and kinetic energy are both conserved—but the collision isn't head-on, so forces act perpendicular to the line joining their centers. The key insight is that the component of velocity along the line of centers gets exchanged (like a head-on collision), while the perpendicular components remain unchanged. This means you'll find two scattering angles by decomposing velocities into radial and tangential parts, then using the geometry of the impact.