Question

Question #dc16a

Answer 1

Positive acceleration is generally meant to mean "speeding up", while negative acceleration is "slowing down", but it can get more complicated than that!

Explanation:

Since acceleration is defined a `a=(Deltav)/(Deltat)`
acceleration will have the same sign that `Deltav` does (as `Deltat` must be positive).

Since `Deltav = v_f-v_i`, `Deltav` will be positive if `v_f>v_i` and will be negative if `v_i >v_f`.

Note: So far, I have ignored the possibility that it might be direction that is included in the sign of the acceleration.
In vertical acceleration problems, it is conventional to refer to the upward direction as positive and the downward direction as negative. This can complicate things, as "going down, slowing down" should be considered as positive acceleration, for example, as it is negative `Deltav` and negative direction = positive acceleration! Here is a list of possibilities:

• going up, speeding up = positive acceleration
• going up, slowing down = negative acceleration
• going down, speeding up = negative acceleration
• going down, slowing down = positive acceleration