Speed-Time Graphs (Cambridge O Level Physics)

• A speed-time graph shows how the speed of a moving object varies with time
  • The red line represents an object with increasing speed
  • The green line represents an object with decreasing speed

Increasing and decreasing speed

Increasing and decreasing speed represented on a speed-time graph

Acceleration on a Speed-Time Graph

• Speed-time graphs also show the following information:
  • If the object is moving with a constant acceleration or deceleration
  • The magnitude of the acceleration or deceleration

• A straight line represents constant acceleration
• The slope of the line represents the magnitude of acceleration
  • A steep slope means large acceleration (or deceleration) - i.e. the object's speed changes very quickly
  • A gentle slope means small acceleration (or deceleration) - i.e. the object's speed changes very gradually
  • A flat line means the acceleration is zero - i.e. the object is moving with a constant speed

  Acceleration, deceleration and constant speed

This image shows how to interpret the slope of a speed-time graph

• The distance travelled by an object can be found by determining the area beneath the graph

 Area under a velocity-time graph

The distance travelled can be found from the area beneath the graph

• If the area beneath the graph forms a triangle (the object is accelerating or decelerating) then the area can be determined using the formula:

• If the area beneath the graph is a rectangle (constant velocity) then the area can be determined using the formula: