I don't get it, why is the graph always linear? Shouldn't its slope be zero when the ball is at the top and stops there for a moment? The way it is "explained" is that it's at the top for instantaneous moment. Okay, but, if let's say, ball was going upward for a 5 sec, then stopped for 1 second and went downwards. Wouldn't you agree with me, that if we were to record the ball's motion, and compared its velocity between 3 and 4 seconds, the difference would be much higher than if we compared velocity between 5 and 6 seconds (when the ball's velocity isn't changing, it simply hangs in the air, therefore there would be no difference in velocity between 5s and 6s)?? If so, then it should be reflected on the graph, considering that the scale is fixed.