On a position-time graph, a line can only do three things — and each one maps to a real motion.
🧭 Plot Summary
A position-time graph plots where an object is (x, vertical axis) against when it's there (t, horizontal axis). Once you can read one fluently, you can extract an entire motion story — starting position, direction, speed, stops, and reversals — without a single sentence of description.
The two skills that unlock everything else: reading a single point on the graph (what was the position at this specific time?), and reading the shape of the line between two points (rising, falling, or flat — and how steep). Steepness of the line and speed of the object turn out to be the same idea in disguise: the steeper the line, the faster the motion.
What you will do in this lesson
- Read position, x, off the vertical axis for any time, t, on the horizontal axis.
- Connect the direction a line rises or falls to the direction an object is actually moving.
- Connect the steepness of a line to how fast an object is moving — steeper is faster, flat is stopped.
- Compare two objects graphed on the same axes, including where their paths cross.
- Translate back and forth between a motion story in words and its position-time graph.
Why it matters
Project 1-1-4: Motion Detector Graph Match hands you a target position-time graph and asks you to reproduce it with your own body in front of a sensor. If you can't read a graph — tell fast from slow, "toward" from "away," stopped from still-in-motion — you can't even start that project, let alone succeed at it. This lesson is the reading practice that makes the project possible.
✅ Self-Check Before You Roll On
Check off each item as you get there. These are not grades — they are your own signal.