accelerationdifferentiationkinematicstimevelocity
This is a screenshot from the lecture about the analysis of various velocity-time graphs I was watching.
I understand that
the concavity of velocity-time graph will tell about the
increasing or decreasing nature of acceleration.
Therefore, this graph must have decreasing acceleration with time since the curve is clearly concave downwards.
Then, why it is written "increasing acceleration" ?
No, all your reasoning is totally right. The conclusion isn't that the graphs are wrong, it's that the time of impact is less than 0.1 second. In this video, for example, the time of impact is just about 0.01 seconds.
Your diagram is incorrect. The objects always experiences negative acceleration, except for the brief moment when it bounces. The negative acceleration always reduces the speed (taking it from positive to negative), but during the impact the speed abruptly switches from negative to positive. The position is what you expect, with the object bouncing up and down in a parabola vs. time.
I drew a crude acceleration (red), velocity (blue) and position (orange) chart below for illustration.
Best Answer
Instead of concave or convex it's easier to note the change in the gradient of the graph to see how the acceleration changes. Here the acceleration ( the gradient of the curve) has a low negative ( suppose -1) then it becomes steeper with time so it has a negative value of larger magnitude ( suppose -4). Thus the magnitude of the acceleration is increasing. Thus you are right as the absolute acceleration is ofcourse decreasing. Hope I could help.