accelerationWatch this thread
Negative acceleration when speed is decreasing, also called deceleration.
In circular motion acceleration can be referred to as centripetal acceleration
Negative acceleration does not mean deceleration. It simply means the direction of acceleration is in the opposite direction to the pre defined positive direction.
Thus, if the velocity and acceleration are both negative, the object is not decelerating. Its speed is actually increasing in the opposite direction to the pre defined positive.