A visualization of a classic related rates problem - a man walking away from a lamppost.
Homer Simpson, who is 6ft tall, is walking away from a 18ft tall lamp post at a speed of 8ft/s. How fast is the tip of his shadow moving along the ground when he is 100ft from the lamp post?

In the distance versus time plot notice that DistHomerPlot (which is the distance Homer is from the lamp post at time t) is a straight line.

Why is it a line?

What is the slope of this line?

The plot ShadowTipPlot (which is the distance the tip of the shadow is from the lamp post at time t) is also a straight line.