Height as a function of time results in... Height. Delta height divided by Delta time is average speed. This is basic math.

If this was speed, there would be points of negative speed, when height is lower at a greater time.

I'm going to assume you're just a troll, nobody can be so dumb.

Edit: just as an observation, if you want to look at the speed, the truncated axis is irrelevant, because the intersection value is derived to 0. You really don't know this?