Calculus exists to solve the rate of change of variables. From a mathematical point of view, it is to study the role of variables in functions. From a physical point of view, it is to solve the definition of speed and acceleration.

The word "change" is the biggest implication of calculus. We should understand mathematics from a philosophical point of view, rather than simply knowing how to calculate. All mathematical abilities will eventually rise to their own philosophy, thus achieving the unity of man and nature.

Calculus is a concept introduced when people can't solve complex sports problems.

Take the definition of induced electromotive force in high school physics as an example. E= the number of broken coils multiplied by the change of magnetic flux compared with last time. In fact, the change of magnetic flux compared with the last time is the derivative of magnetic flux, which is commonly called the rate of change of magnetic flux.

The practical application of calculus is infinitesimal method.

Let's change dX a little.

Apply a classical physical formula and list an equation in this small change.