There are two frequently used graphs of motion: 1) displacement - time and 2) velocity - time.
The slope of a line on a graph of displacement - time refers to velocity.
The slope of a line on a graph of velocity - time refers to acceleration.
The slope is run/rise = Δ f(t) / Δt
So, in the displacement - time graph the slope is change of position / time elapsed, which is the definition of velocity.
While in the velocity - time graph the slope is change of velocity / time elapsed, which is the definition of acceleration.
