How is inertial mass defined?

Inertial mass is defined as the ratio of force applied to an object and the acceleration that the object experiences as a result of that force. This relationship is central to 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, when you rearrange this formula (F = ma) to isolate mass, you get mass (inertial mass) equals force divided by acceleration (m = F/a). This means that the correct definition of inertial mass directly relates to how much force is needed to accelerate an object at a given rate, confirming that it is accurately expressed as force divided by acceleration.