Identify the object of interest. this is the object whose motion you wish to study. draw a picture of the situation. show the object of interest and all other objects—such as ropes, springs, and surfaces—that touch it. draw a closed curve around the object. only the object of interest is inside the curve; everything else is outside. locate every point on the boundary of this curve where other objects touch the object of interest. these are the points where contact forces are exerted on the object. name and label each contact force acting on the object. there is at least one force at each point of contact; there may be more than one. when necessary, use subscripts to distinguish forces of the same type. name and label each long-range force acting on the object. for now, the only long-range force is weight.