Im not sure how to do this. Dont mind some of the numbers in there they are just guesses. I would think it would speeding down when the red line is going toward negative and speeding up when its going positive but i guess not Any ideas?
suppose that you need to draw the curve's tangent line and track the varying trend of the tangent slope k. then the particle is speeding up if its absolute value |k| is increasing, or the particle is slowing down.
This is because |k| relates to |delta S|/|delta t|, i.e., velocity.