# Speed-Time Graphs

• Speed-time graphs represent how the speed of an object changes over a period of time.

• The horizontal axis (‘x’ axis) represents time, normally in seconds (s) or minutes (m), while the vertical axis (‘y’ axis) represents speed, usually in metres per second (m/s) or kilometres per hour (km/h).

• If the graph line is horizontal (parallel to the time axis), this means the speed is constant. The object is moving at a steady speed.

• If the graph line rises, the speed is increasing. This indicates acceleration.

• If the graph line falls, the speed is decreasing, indicating deceleration or slowing down.

• The steeper the line on a speed-time graph, the greater the acceleration or deceleration.

• The gradient of a speed-time graph represents acceleration or deceleration. This can be calculated using the formula: “change in speed ÷ change in time”.

• Area under the graph line represents the total distance travelled.

• If the graph line resets to zero, this indicates that the object has stopped.

• By segmenting the graph and calculating individual areas, we can determine the distance travelled during various stages of motion.

• Remember that speed cannot be negative in a speed-time graph. If dealing with different directions, use separate graphs.

• Ensure to check units consistently in questions involving converting units of speed or time.

• Exercise caution with graphs that contain curves as this represents changing acceleration.

• Keep practicing drawing and interpreting various speed-time graphs to strengthen your understanding and to be prepared for different scenarios in assessments.