The oft-repeated questions when we study motion would be something like "what has mass (or weight) got to do with the motion of a body? What are the effects of friction and surface type would be having on the body? And what's the difference between kinematics and dynamics?
Well, in kinematics, we're studying the quality of motion itself, in terms of distance or displacement, speed or velocity, and acceleration. The mass (or weight) of the object don't come into play here.
What about dynamics then? It's about the study of forces that affect the motion of a body and what are the role of each and every one of these forces; hence introducing the concept of net force and provide evidence for the existence of inertia.