An object which moves in the negative direction has a negative velocity. If the object is speeding up then its acceleration vector is directed in the same direction as its motion (in this case, a negative acceleration).

Why can velocity be negative but speed can t?

Because it is a scalar quantity, it can never be negative. The change in speed can be negative, but not speed itself. Velocity is the rate at which an object's position changes. ... A negative velocity means the object is moving down, backward, or to the left.

Is the velocity negative or positive?

Velocity is positive if an object is moving to the right and it is negative if an object is moving to the left. Speed tells how fast an object is moving without saying anything about its direction. Speed is always positive. Speed is the "absolute value" of the velocity.