Ontario Grade 9 Science Class Practice Exam

A force is best defined as an interaction that causes an object to change its velocity. This definition encompasses a wide range of physical occurrences, including starting movement, stopping movement, or changing the direction of an object's motion.

In physics, force can lead to acceleration or deceleration, which corresponds directly to changes in velocity. This fundamental concept is illustrated in Newton's second law of motion, which states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. Therefore, a force effectively alters the state of motion of an object, making this option the most accurate and comprehensive.

The other options do not encapsulate the full essence of what a force is. For instance, forces are not limited to changing color or exclusively interacting with magnets or living organisms, as forces can act on any physical object, including inanimate ones. This broader application is what makes the definition revolving around velocity the most appropriate choice.