This document defines and explains key concepts related to motion, including: - Motion is defined as a change in position over time. A point of reference is used to measure an object's changing position. - Displacement refers to the straight line distance and direction between two positions, while distance is the total path traveled. - Speed is defined as distance divided by time and can be measured in units like km/h or m/s. Speed with direction is called velocity. - Instantaneous speed is an object's speed at a moment in time, which may vary, while average speed represents the speed over the entire journey. Constant speed means the instantaneous speed does not change. - A