Speed vs. Time

When a ball is thrown vertically upwards and lands back down to the ground, why the speed time graph is a V shape and not a curve? How do you know that the speed is decreasing at a constant rate as it reaches the highest point?
- Lyn (age 13)
Singapore

It's easier to think of the velocity vs. time graph. It's just a straight line, because the acelration is constant. So peed is the absolute value of velocity, s=|v|. If the velocity happens to go through zero, the graph that was following a line sloping down now follows a similar line going up. You can find out how the velocity changes over time in a variety of ways. One of them is to take many pictures as the motion happens, so you can plot position vs. time. The change in position per time gives the velocity, which you can now write down as a function of time. 

Mike W.

(published on 02/16/2015)