Which term refers to a change in speed or direction?

The term that refers to a change in speed or direction is acceleration. Acceleration is defined as the rate of change of velocity over time. It occurs whenever an object's speed increases or decreases, or its direction alters. For example, when a car speeds up as it goes down a hill or slows down when it approaches a stoplight, it is experiencing acceleration. Similarly, if a car makes a turn, even if its speed remains constant, it is still accelerating because it is changing direction.

Velocity, on the other hand, describes the speed of an object in a specific direction but does not inherently denote any change. Momentum relates to the quantity of motion an object has, which is dependent on both its mass and velocity, and does not directly address changes in those quantities. Force is any interaction that, when unopposed, will change the motion of an object, and while it can cause changes in speed or direction, it is not synonymous with such changes itself. Thus, acceleration is the correct term for a change in speed or direction.