# Inertia

**inertialinertia forceinertial forcesprinciple of inertiagravitational massimpetusinertia forcesinertial effectsinertial loadsinertial mass**

Inertia is the resistance, of any physical object, to any change in its velocity.wikipedia

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### Mass

**inertial massgravitational massweight**

Inertia is one of the primary manifestations of mass, which is a quantitative property of physical systems.

Mass is both a property of a physical body and a measure of its resistance to acceleration (a change in its state of motion) when a net force is applied.

### Force

**forcesattractiveforce vector**

The principle of inertia is one of the fundamental principles in classical physics that are still used today to describe the motion of objects and how they are affected by the applied forces on them.

By the early 20th century, Einstein developed a theory of relativity that correctly predicted the action of forces on objects with increasing momenta near the speed of light, and also provided insight into the forces produced by gravitation and inertia.

### John Philoponus

**John PhiloponosPhiloponusJoannes Grammaticus Philoponus**

In the 6th century, John Philoponus criticized the inconsistency between Aristotle's discussion of projectiles, where the medium keeps projectiles going, and his discussion of the void, where the medium would hinder a body's motion.

He was one of the first to propose a "theory of impetus" similar to the modern concept of inertia over Aristotelian dynamics.

### Newton's laws of motion

**laws of motionNewton's second lawNewton's second law of motion**

The term "inertia" is more properly understood as shorthand for "the principle of inertia" as described by Newton in his First Law of Motion: an object not subject to any net external force moves at a constant velocity.

Newton's first law is often referred to as the law of inertia.

### Jean Buridan

**BuridanBuridan, JeanJohn Buridan**

In the 14th century, Jean Buridan rejected the notion that a motion-generating property, which he named impetus, dissipated spontaneously.

He developed the concept of impetus, the first step toward the modern concept of inertia and an important development in the history of medieval science.

### Galileo Galilei

**GalileoGalileanGalilei**

Galileo, in his further development of the Copernican model, recognized these problems with the then-accepted nature of motion and, at least partially as a result, included a restatement of Aristotle's description of motion in a void as a basic physical principle:

Galileo studied speed and velocity, gravity and free fall, the principle of relativity, inertia, projectile motion and also worked in applied science and technology, describing the properties of pendulums and "hydrostatic balances", inventing the thermoscope and various military compasses, and using the telescope for scientific observations of celestial objects.

### Albert of Saxony (philosopher)

**Albert of SaxonyAlbertAlbert III of Saxony**

Buridan's thought was followed up by his pupil Albert of Saxony (1316–1390) and the Oxford Calculators, who performed various experiments that further undermined the classical, Aristotelian view.

This theory was a precursor to the modern theory of inertia.

### Dennis W. Sciama

**Dennis SciamaSciamaD.W. Sciama**

Dennis Sciama later showed that the reaction force produced by the combined gravity of all matter in the universe upon an accelerating object is mathematically equal to the object's inertia, but this would only be a workable physical explanation if, by some mechanism, the gravitational effects operated instantaneously.

Sciama earned his PhD in 1953 at the University of Cambridge supervised by Paul Dirac, with a dissertation on Mach's principle and inertia.

### Johannes Kepler

**KeplerKepler, Johannesdioptrice**

The term "inertia" was first introduced by Johannes Kepler in his Epitome Astronomiae Copernicanae (published in three parts from 1617–1621); however, the meaning of Kepler's term (which he derived from the Latin word for "idleness" or "laziness") was not quite the same as its modern interpretation.

In the late 17th century, a number of physical astronomy theories drawing from Kepler's work—notably those of Giovanni Alfonso Borelli and Robert Hooke—began to incorporate attractive forces (though not the quasi-spiritual motive species postulated by Kepler) and the Cartesian concept of inertia.

### Coriolis force

**Corioliscoriolis effectCoriolis forces**

An observer would see it apparently deflected away from its target by a force (the Coriolis force), but in reality, the southerly target has moved because earth has rotated while the missile is in flight.

However, the Coriolis force is a consequence of inertia, and is not attributable to an identifiable originating body, as is the case for electromagnetic or nuclear forces, for example.

### General relativity

**general theory of relativityrelativitygeneral relativity theory**

In an attempt to address this limitation, Einstein proceeded to develop his general theory of relativity ("The Foundation of the General Theory of Relativity," 1916), which ultimately provided a unified theory for both inertial and noninertial (accelerated) reference frames.

At the base of classical mechanics is the notion that a body's motion can be described as a combination of free (or inertial) motion, and deviations from this free motion.

### Isaac Beeckman

**BeeckmanIsaac Beeckman’s**

The first physicist to completely break away from the Aristotelian model of motion was Isaac Beeckman in 1614.

Beeckman is mentioned to be one of the first persons describing inertia correctly, however he also assumes that a constant circular velocity is conserved.

### Angular momentum

**conservation of angular momentumangular momentamomentum**

Its angular momentum is unchanged, unless an external torque is applied; this is also called conservation of angular momentum.

Many problems in physics involve matter in motion about some certain point in space, be it in actual rotation about it, or simply moving past it, where it is desired to know what effect the moving matter has on the point—can it exert energy upon it or perform work about it? Energy, the ability to do work, can be stored in matter by setting it in motion—a combination of its inertia and its displacement.

### Theory of relativity

**relativityrelativisticrelativity theory**

This was clear at the beginning of the 20th century, before the advent of the theory of relativity.

The upshot of this is that free fall is inertial motion: an object in free fall is falling because that is how objects move when there is no force being exerted on them, instead of this being due to the force of gravity as is the case in classical mechanics.

### Mach's principle

**Machiandistant masses of the universeMach principle**

Mach's principle

It is often stated in vague ways, like "mass out there influences inertia here".

### Inertial frame of reference

**inertial frameinertialinertial reference frame**

Albert Einstein's theory of special relativity, as proposed in his 1905 paper entitled "On the Electrodynamics of Moving Bodies" was built on the understanding of inertia and inertial reference frames developed by Galileo and Newton.

Within the realm of Newtonian mechanics, an inertial frame of reference, or inertial reference frame, is one in which Newton's first law of motion is valid.

### Epitome Astronomiae Copernicanae

The term "inertia" was first introduced by Johannes Kepler in his Epitome Astronomiae Copernicanae (published in three parts from 1617–1621); however, the meaning of Kepler's term (which he derived from the Latin word for "idleness" or "laziness") was not quite the same as its modern interpretation.

The term "inertia" was first introduced in the Epitome.

### Kinetic energy

**kinetickinetic energiesorbital velocity**

Kinetic energy

(In this equation the moment of inertia must be taken about an axis through the center of mass and the rotation measured by ω must be around that axis; more general equations exist for systems where the object is subject to wobble due to its eccentric shape).

### Classical mechanics

**classicalNewtonianNewtonian physics**

Since initial publication, Newton's Laws of Motion (and by inclusion, this first law) have come to form the basis for the branch of physics known as classical mechanics.

Early versions of the law of inertia, known as Newton's first law of motion, and the concept relating to momentum, part of Newton's second law of motion, were described by Ibn al-Haytham (Alhazen) and Avicenna.

### Physical body

**objectbodyphysical object**

Inertia is the resistance, of any physical object, to any change in its velocity.

### Velocity

**velocitiesvelocity vectorlinear velocity**

Inertia is the resistance, of any physical object, to any change in its velocity.

### Speed

**tangential velocityaverage speedtangential speed**

This includes changes to the object's speed, or direction of motion.

### Relative direction

**directionleftdirectional**

This includes changes to the object's speed, or direction of motion.

### Classical physics

**classicalclassical theoryclassically**

The principle of inertia is one of the fundamental principles in classical physics that are still used today to describe the motion of objects and how they are affected by the applied forces on them.

### Physical system

**systemphysical systemsphysical**

Inertia is one of the primary manifestations of mass, which is a quantitative property of physical systems.