Speed-Time Graphs
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Learning Objective
In this lesson we will learn how changes in speed can be represented graphically.
Learning Outcomes
By the end of this lesson you will be able to:
- Describe the layout of a speed-time graph.
- Describe how constant speed, increasing speed, decreasing speed and stationariness are represented on a speed-time graph.
- Describe the relationship between the gradient of the line on a speed-time graph and acceleration.
- Calculate acceleration from a speed-time graph.
- Calculate distance travelled from a speed-time graph.
(Image: PublicDomainPictures, Pixabay)
Lesson Summary
- A speed-time graph plots the speed of an object (on the y-axis) against time (on the x-axis).
- Speed-time graphs can show:
- Stationariness – a horizontal line that lies on the x-axis (y = 0).
- Constant speed – a horizontal line that lies above the x-axis (y > 0).
- Increasing speed (acceleration) – a line with a positive gradient.
- For constant acceleration, the line will be straight.
- Decreasing speed (deceleration) – a line with a negative gradient.
- For constant deceleration, the line will be straight.
- The gradient of the line on a speed-time graph represents acceleration.
- The steeper the slope of the line on a speed-time graph, the greater the acceleration.
- The area under the line on a speed-time graph represents distance travelled.
- For rectangular sections, distance (area) = speed × time.
- For triangular sections, distance (area) = ½ × speed × time.
- For speed-time graphs containing multiple rectangular and triangular sections, the total distance travelled is given by the combined areas of these sections.
(Image: Realbigtaco, Wikimedia Commons)
(Header image: Andrr, Adobe Stock)