The inertia is the tendency of bodies to remain in the state in which they are, rest and livelihoods of uniform rectilinear motion. For example, when starting a car, its occupants are driven back. That is, tend to remain at rest due to inertia. By contrast, when the vehicle stops, the occupants themselves tend to move forward, that is, to continue moving. The principle of inertia was raised initially by the physicist Isaac Newton. His first law states precisely that every body remains at rest or in uniform rectilinear motion until acted upon by a force that do change state.
On moving bodies, as well inertia, friction acts. If, for example, throw a ball in the air, this, according to the principle of inertia would have to keep moving indefinitely. But it ends a halt due to friction, ie the resistance that opposes the medium in which it travels.