What does it mean when the position vs. time graph is below the x-axis?

if the "x" axis is for time, then a negative position means that motion has backed up past where it started.

Everything in physics is arbitrary so you can make it whatever you want.

When the position vs. time graph is below the x-axis, it generally means that the object's position is negative. In other words, the object is located in the negative direction according to the chosen coordinate system. The x-axis represents the position, and the y-axis represents time. When the graph is below the x-axis, it indicates that the object has moved or is located in the negative direction relative to the reference point or the starting position.

When the position vs. time graph is below the x-axis, it means that the object's position is in the negative direction of the x-axis. In physics, the x-axis is often used to represent the direction of motion or position, with positive values indicating motion or position in one direction and negative values indicating motion or position in the opposite direction.

To understand the position vs. time graph, it's important to know how it is plotted. The x-axis represents time, while the y-axis represents position. Each point on the graph corresponds to a specific time and the corresponding position of the object at that time.

When the graph is below the x-axis, it indicates that the object has a negative position with respect to the reference point or origin. For example, if the origin is at 0 and the object is positioned at -5, it means that the object is located 5 units in the negative direction from the reference point.

Interpreting a position vs. time graph allows us to understand an object's direction of motion and changes in its position over time. By observing the graph, we can determine whether an object is moving forward (positive region of the graph) or backward (negative region of the graph), as well as its speed or velocity.