Why when an object keeps moving at a constant acceleration, it's speed is not always greater than 0?

  • $\begingroup$ Can you please edit your question to elaborate a bit, maybe adding a concrete example? As of now, at least I am really struggling to understand your question. $\endgroup$
    – Sanya
    Oct 30, 2016 at 9:13
  • 1
    $\begingroup$ Typically, a negative velocity just refers to the direction of the object. Like throwing a ball straight upwards; once released, it is constantly accelerating down due to gravity, but it is still moving upwards until it's velocity reaches 0, and then begins to fall. While the ball travels upwards, its velocity is positive, acceleration is negative. While the ball travels downwards, its velocity is negative as it's accelerating with the gravity field. $\endgroup$
    – bleuofblue
    Oct 30, 2016 at 9:25
  • $\begingroup$ Consider this question: "Can the temperature be negative while it is increasing"? $\endgroup$
    – Steeven
    Oct 30, 2016 at 9:27

1 Answer 1


I'm not sure I understood your question. If you have an object that has an initial velocity $v_i\neq0$ and has an acceleration directed in the opposite direction of the motion, the object will start decreasing velocity. At a certain point it will reach $v=0$ and after, eventually, it will move backwards.


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