Distance-time graphs

• Distance is a scalar quantity
• Distance


  A measure of how far something has moved, but not the direction
• If an object moves in a straight line, you can show the distance it travels using a distance-time graph
• The distance-time graph in Figure 1 shows a runner's journey
• The runner starts off fast

  Slows down to a walking pace, and finally stops
• Runner's journey segments


  1. A to B: Running

  2. B to C: Walking

  3. C to D: Resting
• The runner has sprinted 60 m in just 10 seconds
• The runner walked 30 m in 20 seconds
• The runner has not moved for 20 seconds
• Distance-time graph


  Tells you whether an object is moving or not, and how fast it is moving
• Horizontal line


  Means the object is not moving
• Diagonal line


  Means it is moving at a constant speed
• Steeper slope


  Indicates faster speed
• You can calculate the speed using values from the distance-time graph
• The x-axis of a distance-time graph tells you how much time has passed
• The y-axis tells you the distance travelled
• Calculating speed from a distance-time graph

  1. Work out the steepness of the graph (gradient)

  2. Divide the y-axis by the x-axis (distance by time)
• A distance-time graph is a useful way of describing the motion of an object
• Constant speed


  The line is diagonal
• Stopped moving


  The line is horizontal
• Faster object


  The steeper the slope of the line
• Figure 2 is a distance-time graph of a journey
• Calculate the total distance travelled
• Calculate the average speed for the 40s journey
• Give the units