2-4 Acceleration (VECTOR) Acceleration is… the rate of change of velocity.
Acceleration is a vector, although in one-dimensional motion we only need the sign. The previous image shows positive acceleration; here is negative acceleration:
Difference between negative acceleration and deceleration (I will not be picky about this): Negative acceleration is acceleration in the negative direction as defined by the coordinate system. Deceleration occurs when the acceleration is opposite in direction to the velocity.
2-4 Instantaneous Acceleration (2-5) Example (board or OneNote): A particle is moving with a velocity of 60.0 m/s in the positive x direction at t=0. Between t=0 and t=15.0 s, the velocity decreases uniformly to zero. What was the acceleration during this 15.0-s interval? What is the significance of the sign of your answer?