Which of the following defines acceleration in physics?

Acceleration in physics is defined as the change in velocity over time. It describes how quickly an object's velocity is changing, which can include changes in speed or direction. Velocity is a vector quantity that encompasses both the speed and direction of an object, so acceleration can indicate whether an object is speeding up, slowing down, or changing direction.

When an object has a uniform velocity, if it begins to speed up or slow down, it is experiencing acceleration. This concept is fundamental in kinematics, the branch of mechanics that deals with the motion of objects without considering the forces that cause this motion.

The other choices refer to concepts that are different from acceleration. Change in force over time relates more to how forces interact but does not specifically capture how objects change their motion. Change in position over time refers to velocity itself, not acceleration, and change in energy over time pertains to work or power rather than how motion changes. Thus, option B precisely captures the essence of acceleration in the context of motion.