What term describes a change in an object's speed or direction?

The term that describes a change in an object's speed or direction is acceleration. Acceleration is defined as the rate at which an object changes its velocity. This means that it not only encompasses increases in speed but also includes decreases in speed (deceleration) and any change in direction, with the latter being especially significant when considering objects moving in circular paths or changing their course.

Velocity, while related, specifically refers to the speed of an object in a given direction. Force is a different concept that pertains to an interaction capable of changing an object's motion, as described by Newton's laws of motion. Momentum involves the quantity of motion an object has, which is a product of its mass and velocity, but it does not describe changes in speed or direction directly. Thus, acceleration is the most accurate term for the scenario presented in the question.