o Emphasis of this section 1 What is a suitable model of the fluid? 2 How do we visualize this squishy substance in order to apply the three fundamental principles? 3. Three different mode/s most/y used to deal with aerodynam/cs. finite contro/ volume(有限控制体) infinitesimal/ fuid element(无原小流体微团) molecular(自由分子)Emphasis of this section: 1. What is a suitable model of the fluid? 2. How do we visualize this squishy substance in order to apply the three fundamental principles? 3. Three different models mostly used to deal with aerodynamics. finite control volume （有限控制体） infinitesimal fluid element （无限小流体微团） molecular （自由分子）