Mechanics

Displacement (s) The straight-line distance from the starting point to the final point, with direction. Unlike distance (a scalar), displacement is a vector. For example, a runner completing one lap of a 400 m track has a displacement of zero, but has travelled a distance of 400 m. Velocity (v) The rate of change of displacement with respect to time. Average velocity = total displacement / total time. Instantaneous velocity is the velocity at a specific instant. A car moving north at 20 m/s has a velocity of +20 m/s (if north is positive); if it turns south, its velocity becomes negative. Acceleration (a) The rate of change of velocity with respect to time. If velocity increases, acceleration is positive; if velocity decreases, acceleration is negative (deceleration). For example, a ball dropped from rest accelerates at 9.81 m/s² downward due to gravity.