Newton's first law of motion in the context of "Physical laws"

Principles of Philosophy (Latin: Principia Philosophiae) is a book by the French philosopher and scientist René Descartes. In essence, it is a synthesis of the Discourse on Method and Meditations on First Philosophy. It was written in Latin, published in 1644 and dedicated to Elisabeth of Bohemia, with whom Descartes had a long-standing friendship. A French version (Les Principes de la Philosophie) followed in 1647.

The book sets forth the principles of nature—the laws of physics—as Descartes viewed them. Most notably, it set forth the principle that in the absence of external forces, an object's motion will be uniform and in a straight line. Isaac Newton borrowed this principle from Descartes and included it in his own Principia; to this day, it is still generally referred to as Newton's first law of motion. The book was primarily intended to replace the Aristotelian curriculum then used in French and British universities. The work provides a systematic statement of his metaphysics and natural philosophy, and represents the first truly comprehensive, mechanistic account of the universe.

Linear motion, also called rectilinear motion, is one-dimensional motion along a straight line, and can therefore be described mathematically using only one spatial dimension. The linear motion can be of two types: uniform linear motion, with constant velocity (zero acceleration); and non-uniform linear motion, with variable velocity (non-zero acceleration). The motion of a particle (a point-like object) along a line can be described by its position ${\displaystyle x}$, which varies with ${\displaystyle t}$ (time). An example of linear motion is an athlete running a 100-meter dash along a straight track.

Linear motion is the most basic of all motion. According to Newton's first law of motion, objects that do not experience any net force will continue to move in a straight line with a constant velocity until they are subjected to a net force. Under everyday circumstances, external forces such as gravity and friction can cause an object to change the direction of its motion, so that its motion cannot be described as linear.