Definition of Inertia and Mass
Inertia is the natural tendency of an object to remain at rest or in motion at a constant velocity. The mass of an object is a quantitative measure of inertia
SI Unit of Inertia and Mass: kilogram (Kg)
在左边的汽车安全带原理图里我们可以得出：
Inertia plays a central role in one seat-belt mechanism. The grey part of the drawing applies when the car is at rest or moving at a constant velocity. The coloured parts show what happens when the car suddenly slows down, as in an accident.