When can holistic analysis be used to study mechanics in senior high school

When can holistic analysis be used to study mechanics in senior high school

Take several objects as a whole. Then the interaction force between these objects can not be calculated. When accepting the analysis, only the force exerted on the whole by other objects is analyzed. For example, when a person sits on the chair of the bus, the chair is fixed on the bus. By using the whole analysis, the force exerted on the whole of the bus is gravity, the support force and friction force of the ground, We don't consider the interaction between people, chairs and buses