# Inertia

Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. The principle of inertia is one of the fundamental principles of classical physics which are used to describe the motion of matter and how it is affected by applied forces. Inertia comes from the Latin word, iners, meaning idle, or lazy. Isaac Newton defined inertia as his first law in his Philosophiæ Naturalis Principia Mathematica, which states:

The vis insita, or innate force of matter, is a power of resisting by which every body, as much as in it lies, endeavours to preserve its present state, whether it be of rest or of moving uniformly forward in a straight line.

In common usage the term "inertia" may refer to an object's "amount of resistance to change in velocity" (which is quantified by its mass), or sometimes to its momentum, depending on the context. The term "inertia" is more properly understood as shorthand for "the principle of inertia" as described by Newton in his First Law of Motion; that an object not subject to any net external force moves at a constant velocity. Thus an object will continue moving at its current velocity until some force causes its speed or direction to change.

On the surface of the Earth inertia is often masked by the effects of friction and air resistance, both of which tend to decrease the speed of moving objects (commonly to the point of rest), and gravity. This misled classical theorists such as Aristotle, who believed that objects would move only as long as force was applied to them.

Read more about Inertia:  Source of Inertia, Rotational Inertia

### Other articles related to "inertia":

Rotational Inertia
... Another form of inertia is rotational inertia (→ moment of inertia), which refers to the fact that a rotating rigid body maintains its state of uniform rotational motion ... Rotational inertia depends on the object remaining structurally intact as a rigid body, and also has practical consequences For example, a gyroscope uses the property that it resists any change in the ...
True Polar Wander
... In a stable state, the largest moments of inertia axis is aligned with the spin axis, with the smaller two moment of inertia axes lying in the plane of the equator ... will occur the planet or moon will rotate as a rigid body to realign the largest moment of inertia axis with the spin axis ...
Morison Equation - Description
... The Morison equation is the sum of two force components an inertia force in phase with the local flow acceleration and a drag force proportional to the (signed) square of the instantaneous flow velocity ... The inertia force is of the functional form as found in potential flow theory, while the drag force has the form as found for a body placed in a steady flow ... O'Brien, Johnson and Schaaf these two force components, inertia and drag, are simply added to describe the force in an oscillatory flow ...
Stress-strain Index - History and Relation To Moments of Inertia
... improvement over the information provided by calculating the area moments of inertia and polar moments of inertia ...
List Of Area Moments Of Inertia
... The following is a list of area moments of inertia ... The area moment of inertia or second moment of area has a unit of dimension length4, and should not be confused with the mass moment of inertia ... If the piece is thin, however, the mass moment of inertia equals the areal density times the area moment of inertia ...

### Famous quotes containing the word inertia:

What is wrong with priests and popes is that instead of being apostles and saints, they are nothing but empirics who say “I know” instead of “I am learning,” and pray for credulity and inertia as wise men pray for scepticism and activity.
George Bernard Shaw (1856–1950)