In a distance-time graph, what does a horizontal line indicate?

In a distance-time graph, a horizontal line indicates that the distance travelled by an object does not change over time. This means that the object is at rest and not moving. When the graph is horizontal, the time is increasing, but the distance remains constant, which confirms that the object's speed is zero. Consequently, the correct interpretation of a horizontal line in this context is that the object is stationary.

In contrast, a line that slopes upwards represents a constant speed as the distance increases with time, while a line that slopes downwards would indicate a decrease in distance, meaning the object is moving back toward the starting point. An accelerating object would be represented by a curve that gets steeper over time, showing an increase in speed.