A horizontal line on a distance-time graph indicates that the object is stationary.

In a distance-time graph, the x-axis typically represents time, while the y-axis represents distance. When you observe a horizontal line, it signifies that as time progresses, the distance remains unchanged. This indicates that the object is at rest and not moving.

To illustrate this concept, consider the journey of a car plotted on a distance-time graph. If the car stops at a traffic light for a few minutes, the distance it has traveled remains constant during that period. On the graph, this would be represented by a horizontal line, as the distance (on the y-axis) does not change while time (on the x-axis) continues to increase.

From a mathematical perspective, the gradient (or slope) of a line on a distance-time graph represents the speed of the object. A horizontal line has a gradient of zero, which means the speed is also zero. Therefore, the object is not in motion. This contrasts with a sloped line, which indicates that the object is moving at a constant speed, or a curved line, which suggests variations in speed.

In conclusion, whenever you see a horizontal line on a distance-time graph, you can confidently assert that the object is stationary during that time interval. This is a fundamental concept in understanding motion and interpreting graphs in GCSE Maths.