Transcript Physics 111
Chapter 9, System of Particles Center of Mass Momentum and Conservation Impulse Rocket Center of Mass for a System of Particles The center of mass of a body or a system of bodies moves as though all of the mass were concentrated there and all external forces were applied there. 2 bodies, 1 dimension n bodies, 3 dimensions n bodies, 3 dimensions, vector equation Center of Mass for a Solid Body Differential mass element dm Uniform density Newton’s 2nd Law for a System of Particles System of particles A grand jeté A firework rocket explodes Linear Momentum Particle System Conservation of Linear Momentum If no net external force acts on a system of particles, the total linear momentum P of the system cannot change. If the component of the net external force on a closed system is zero along an axis, then the component of the linear momentum along that axis cannot change. Impulse and Linear Momentum Definition of Impulse Impulse–Linear Momentum Theorem Collision of two particle-like bodies Steady stream of projectiles Momentum and Kinetic Energy Closed system (no mass enters or leaves) Isolated system (no external net force) Elastic collision (kinetic energy conserved) Inelastic collision (kinetic energy not conserved) Completely inelastic collision (bodies always stick together) In a closed, isolated system containing a collision, the linear momentum of each colliding body may change but the total momentum P of the system cannot change, whether the collision is elastic or inelastic. Inelastic Collisions in 1D Conservation of Linear Momentum Completely Inelastic Collision Velocity of Center of Mass Elastic Collisions in 1D In an elastic collision, the kinetic energy of each colliding body may change, but the total kinetic energy of the system does not change. Stationary Target Moving Target Other Applications Sample Problem 9-8, 9-10 Rocket System Rocket equations