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Speed-time graphs

A speed-time graph shows the time on the x-axis and speed on the y-axis.

The gradient of the graph gives the acceleration.

  • A horizontal line indicates that the object is moving at a constant velocity.
  • A positive gradient indicates that the object is accelerating.
  • A negative gradient indicates that the object is decelerating.
  • A curved line indicates non-uniform acceleration.
 The graph shows a vehicle accelerating and then driving at a constant speed before decelerating until stopped

The area under the graph indicates the distance travelled.

To work out the distance travelled during $$\Tblue{\text{section A}}$$ on the graph we need to find the area of the triangle underneath the graph. $$$\Tblue{\text{distance}} = \frac{1}{2} \times 10 \us \times 20 \umps = 100 \um$$$

The distance travelled during $$\Tred{\text{section B}}$$ is equal to the area of the rectangle under the graph. $$$\Tred{\text{distance}} = 10 \us \times 20 \umps = 200 \um$$$

The total distance travelled is equal to the sum of the three sections $$$\text{total distance} = 100 \um + 200 \um + 200 \um = 500 \um.$$$