Distance-Time Graphs (Cambridge O Level Physics)

• A distance-time graph shows how the distance of an object moving in a straight line (from a starting position) varies over time:

Distance-time graph

This graph shows a moving object moving further away from its origin

Constant Speed on a Distance-Time Graph

• Distance-time graphs also show the following information:
  • If the object is moving at a constant speed
  • How large or small the speed is

• A straight line represents constant speed
• The slope of the straight line represents the magnitude of the speed:
  • A very steep slope means the object is moving at a large speed
  • A shallow slope means the object is moving at a small speed
  • A flat, horizontal line means the object is stationary (not moving)

Faster and slower speed on a distance-time graph

This graph shows how the slope of a line is used to interpret the speed of moving objects. Both of these objects are moving with a constant speed, because the lines are straight.

Changing Speed on a Distance-Time Graph

• Objects might be moving at a changing speed
  • This is represented by a curve

• In this case, the slope of the line will be changing
  • If the slope is increasing, the speed is increasing (accelerating)
  • If the slope is decreasing, the speed is decreasing (decelerating)

• The image below shows two different objects moving with changing speeds

Acceleration and deceleration on a distance-time graph

Changing speeds are represented by changing slopes. The red line represents an object slowing down and the green line represents an object speeding up.

• The speed of a moving object can be calculated from the gradient of the line on a distance-time graph:

Gradient of a distance-time graph

The speed of an object can be found by calculating the gradient of a distance-time graph

•  is the change in y (distance) values
•  is the change in x (time) values