To understand horizontal line we need to understand the distance-time graph.
What is a distance-time graph?
The distance-time graph represents the velocity of an object, it shows in what time how much distance is been covered by the object.
What does the horizontal line represent?
The line represents that the object is not traveling therefore, the velocity is zero.
As we can see if the object was moving, the distance on the graph would have also increased but since the line is horizontal, therefore, there is no change in the location of the object but the time is continuously increasing.
hence, the line represents that the velocity of the object is zero.
Learn more about Velocity:
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