Typical examples of inertia include a passenger's body slightly moving backwards when a vehicle suddenly starts; a passenger's body leaning forward when a moving vehicle stops and a passenger's body jerking to the side when a vehicle maneuvers a sharp turn. Inertia is one of the defining characteristics of matter, which refers to the tendency of any object to remain at rest or continuously move along a straight line.
Inertia is classified into three types: inertia of rest, inertia of motion and inertia of direction. A leaf falling from the branch of a tree that is disturbed by a strong wind is an example of inertia of rest. A person that falls down after carelessly jumping off a moving train is an example of inertia of motion. Mud that sticks to rotating wheels and are thrown tangentially is an example of inertia of direction.