5.9 - Distance-Time Graphs

Reading a distance-time graph

• A distance-time graph shows how far an object has travelled from its starting point over time.
• A flat section means the object is stationary (at rest) - the distance doesn't change.
• A straight, sloping section means the object is moving at a steady speed - the steeper the line, the faster it's going.
• A curve means the speed is changing (accelerating or decelerating):
  • A curve that gets steeper means the object is speeding up.
  • A curve that levels off means the object is slowing down.

Finding speed from the gradient

• The gradient (slope) of a distance-time graph at any point equals the speed of the object at that point.
• For non-uniform speed, the average speed is the total distance travelled divided by the total time taken.

Formula for speed

Worked example - Speed from a straight section

A runner moves in a straight line. On a distance-time graph, a straight section of the line rises from 0 m to 40 m between 0 s and 5 s. Calculate the runner's speed during this section.