Which of the following defines a force?

A force is fundamentally defined as a push or pull exerted on an object. This definition captures the essence of how forces interact with objects, influencing their state of motion. A force can cause an object to start moving, stop moving, change direction, or change speed, according to Newton's laws of motion.

When you push a stationary object, you are applying a force that causes it to move, while pulling can involve tension, such as in a rope or cable. The application of force is central to understanding dynamics in physics and engineering.

Other choices, while related to motion, do not define force. For instance, a change in direction of an object's motion describes the effect of force rather than its definition. The mass of an object acting upon another pertains more to gravitational force rather than defining the concept of force itself. Lastly, the speed of an object in a given direction refers to velocity, which describes motion but does not encapsulate the concept of force. Thus, the definition of force as a push or pull accurately encompasses its role in physical interactions.