Based on the Newton’s law of motion, the motion equation of the microscopic car-following model is introduced. The moving vehicles comply with the idea of Newton's equations of motion. But the interaction between vehicles is different from their traction. The inertia of the car is not its mass. We discuss the differences and present how to treat them. This article can deepen and widen the students' understanding of Newton's laws of motion. It can also provide the materials for university physical teaching. It is suitable for the students to exploratory study.