1, differential equation, refers to the relationship with unknown function and its derivative. Solving differential equations means finding unknown functions.
Differential equations are developed by calculus. Newton and Leibniz, the founders of calculus, both dealt with problems related to differential equations in their works. Differential equations are widely used and can solve many problems related to derivatives.
Many kinematics and dynamics problems involving variable forces in physics, such as falling bodies with air resistance as speed function, can be solved by differential equations. In addition, differential equations have applications in chemistry, engineering, economics and demography.
2. Transfer function refers to the ratio of Laplace transform (or Z transform) of response (i.e. output) to Laplace transform of excitation (i.e. input) of linear system under zero initial condition. Let G(s)=Y(s)/U(s), where Y(s) and U(s) are Laplace transforms of output and input respectively. Transfer function is one of the main tools to study classical control theory.
3. The system frame diagram is the overall functional design diagram of the system. The units of the block diagram are all basic units, and the units that simulate the block diagram can be a small system.