This is a visual of the function of sin(x), and it's derivative cos(x).
The real life example of this could be a man riding a bike up a hill, and it compares his position to his velocity. The velocity is the derivative of the position. This graph shows the relationship between sin(x) and cos(x). Notice the position can be negative due to movement around the x-axis.Also notice when sin(x) slope is zero, cos(x) crosses through the x-axis, creating a zero.