Read the shape
Straight, curved or level: what a position-time graph says.
Three vehicles
One vehicle drives steadily. One speeds up from rest. One stands parked by the road. Each one's position is plotted against time.
Do you think the three graphs look alike?
What this lesson covers
The idea
A straight-line position-time graph means constant velocity, a curved one means changing velocity (accelerated motion), and a straight line parallel to the time axis means the object is at rest.
Three vehicles
One vehicle drives steadily. One speeds up from rest. One stands parked by the road. Each one's position is plotted against time.
Do you think the three graphs look alike?
- No, each motion gives its own shape
- Yes, the three graphs look the same
- Yes, the three graphs are all curves
Three shapes
Choose each motion and look at the shape of the graph.
Shape tells the motion
Steady motion gave a straight sloping line, speeding up gave a curve, and the parked vehicle gave a level line. So the shape of a position-time graph tells us the kind of motion.
A straight-line position-time graph means constant velocity. A curved one means the velocity is changing, so the motion is accelerated. A straight line parallel to the time axis means the object is at rest.
Notes
Straight slope: constant velocity. Curved: changing velocity (accelerated). Level (parallel to the time axis): at rest.
Check yourself
A position-time graph is a straight line sloping upward. The object moves with…
A position-time graph is a curve. The motion is…
A vehicle is 40 m from the origin at 0 s, 2 s, 4 s and 6 s. Its position-time graph is…
Which graph shape shows an object that is at rest?
- changing velocity. A curved graph, not a straight one, shows changing velocity.
- constant velocity — correct. Yes!
- zero velocity. A level line, not a sloping one, shows an object at rest.
- at rest. An object at rest gives a line parallel to the time axis.
- steady, with constant velocity. Constant velocity gives a straight line, not a curve.
- accelerated, because the velocity is not constant — correct. Yes!
- a straight line parallel to the time axis — correct. Yes!
- a straight line sloping upward. A sloping line would mean the position changes with time.
- a curve. A curve would mean the velocity is changing, but the vehicle does not move at all.
- A curve bending upward. A curve shows changing velocity, so the object is moving.
- A straight line parallel to the time axis — correct. Yes!
- A straight line sloping upward. A sloping line shows constant velocity, so the object is moving.