Particle dynamics predicts the motion of bodies whose internal size and rotation can be neglected for the question being studied. A point particle has a position and mass; applied forces determine its acceleration through Newton's second law. For fixed mass in an inertial frame, the basic problem iswith an initial position and velocity.
A ball's projectile motion can be approximated this way when its size is small compared with its path and spin has negligible influence. Air drag introduces a velocity-dependent force; contact with a surface may introduce mechanical constraints. The same method extends to interacting particles, where momentum conservation and conservation of energy can simplify the coupled equations of motion.
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