A man stands on a cliff and watches a hot air balloon (the balloon is far away, it's
not just very small). You can click the play/pause button
in the lower left-hand corner of the applet to watch the balloon rise and fall. Two important
questions we'll probe:
- What is the average rate of change of the balloon's height,
between two different moments in time?
- What is the instantaneous rate of change of the balloon's height,
at one particular moment in time?