The correct answer is 2) acceleration.
Acceleration is defined as the rate at which an object changes its velocity. This includes not just speeding up, but also slowing down (which is also referred to as negative acceleration or deceleration) and changing direction. When any of these changes occur, it indicates that the object is experiencing acceleration.
Momentum, on the other hand, is a measure of the motion of an object and is dependent on both its mass and velocity, but it does not specifically describe changes in that motion. Potential energy relates to the energy stored in an object based on its position, and is not directly related to how an object moves or changes its speed or direction.