Inertia
Inertia, the property of matter that causes it to resist any change of its motion in either direction or speed. This property is accurately described by the first law of motion of the English scientist Sir Isaac Newton : An object at rest tends to remain at rest, and an object in motion tends to continue in motion in a straight line unless acted upon by an outside force. For example, passengers in an accelerating automobile feel the force of the seat against their backs overcoming their inertia so as to increase their velocity . As the car decelerates, the passengers tend to continue in motion and lurch forward. If the car turns a corner, then a package on the car seat will slide across the seat as the inertia of the package causes it to continue moving in a straight line. Any body spinning on its axis, such as a flywheel, exhibits rotational inertia, a resistance to change of its rotational speed. To change the rate of rotation of an object by a certain amount, a relatively large forc