Law of Inertia

Early understanding of motion

Prior to the Renaissance, the most generally accepted theory of motion in Western philosophy was based on Aristotle (around 335 BC to 322 BC) who said that, in the absence of an external motive power, all objects (on Earth) would come to rest and that moving objects only continue to move so long as there is a power inducing them to do so.

comes from the Latin word, iners, meaning idle, sluggish. Inertia is one of the primary manifestations of mass, which is a quantitative property of physical systems.

Who’s this Scientist?

Aristotle

Aristotle, and his peripatetic followers, held that a body was only maintained in motion by the action of a continuous external force. Thus, in the Aristotelian view, a projectile moving through the air would owe its continuing motion to eddies or vibrations in the surrounding medium, a phenomenon known as antiperistasis.

Who’s this Scientist?

Galileo Galilei

Galileo writes that ‘all external impediments removed, a heavy body on a spherical surface concentric with the earth will maintain itself in that state in which it has been; if placed in movement towards the west , it will maintain itself in that movement’. This notion which is termed ‘circular inertia’ or ‘horizontal circular inertia’ by historians of science, is a precursor to, but distinct from, Newton’s notion of rectilinear inertia

Who’s this Scientist?

Albert Einstein

Einstein drew on Mach's principle in his original development of special relativity but then abandoned it as unnecessary. Later, Einstein fiercely re-asserted the equivalence of all inertial frames and showed that, once combined with the principle of the constancy of the speed of light, it led to satisfactory explanations of many surprising physical phenomena.

Who’s this Scientist?

Sir Isaac Newton

Sir Isaac Newton first presented his three laws of motion in the "Principia Mathematica Philosophiae Naturalis" in 1686. His first law states that every object remains at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force. This is normally taken as the definition of inertia.

EXAMPLES

According to Newton's first law, the marble on that bottom ramp should just keep going. And going.

According to this, every body preserves its state of rest unless some external force compels it to change its state of rest.

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Prepared by:CJ E. BernalIV – Pasteur