Negative acceleration - change in direction or slowing down?

[kathyt.25]

Homework Statement

Since we can't tell if a value of negative acceleration means a change in direction or decceleration, how WOULD we be able to tell if its a change in direction or the speed is slowing down (say, if we were given v_initial and v_final)?

Homework Equations

The Attempt at a Solution

 

[jgens]

If you're given V_i and V_f you know that some negative acceleration had to occur in the direction of motion. You need more than just velocities however, to determine much of anything about the acceleration. Similarly, if you're just given an acceleration, that doesn't necessarily tell you much about how the velocity changes.

 

[diazona]

Y'know, a negative acceleration could even mean something is speeding up, if it has a negative velocity (i.e. if it's moving "backwards")

 

[Santorican]

I think it has to do with acceleration being the second derivative of the position vector but I am not entirely sure.