Mechanical Motion: Trajectory, Path and Displacement
How do we describe where something is and how far it has gone?
Big Idea: When a body changes its position compared with other bodies as time passes, we say it is in mechanical motion. To describe that motion clearly, physics gives us three simple tools: the trajectory (the line it moves along), the path (how much line it covered), and the displacement (how far and in which direction it ended up from the start).
By the end of this lesson you will be able to:
- say what mechanical motion is and why we always need a reference body;
- explain why motion is relative (a passenger can be moving and standing still at the same time);
- tell a trajectory apart from a path;
- measure the path s in metres and use its symbol;
- understand displacement as a directed segment (a vector) and see how it differs from path.