Newton's laws of motion
Three laws describing motion and force relationships.
Newton's laws of motion are three physical laws that describe the relationship between the motion of an object and the forces acting on it. These laws, which provide the basis for Newtonian mechanics, can be paraphrased as follows: a body remains at rest or in motion at a constant speed in a straight line unless acted upon by a force; at any instant, the net force on a body equals its mass times its acceleration, or equivalently, the rate of change of its momentum; and if two bodies exert forces on each other, those forces have equal magnitude but opposite directions. Isaac Newton first stated these three laws in his work *Philosophiæ Naturalis Principia Mathematica*, originally published in 1687. He used them to investigate and explain the motion of many physical objects and systems. In the time since, new insights, especially concerning the concept of energy, built the field of classical mechanics on his foundations. In modern times, limitations to Newton's laws have been discovered, leading to new theories such as quantum mechanics and relativity to address physics in more extreme cases. The laws are often stated for point or particle masses, where a body's volume is negligible, a reasonable approximation when internal motion can be ignored and separations between bodies are much larger than their sizes. The mathematical description of motion, or kinematics, relies on specifying positions using numerical coordinates, with a body's trajectory represented by a function assigning position coordinates to each time value. Position, velocity, and acceleration are all vector quantities, possessing both magnitude and direction, and vector algebra describes motion in multiple dimensions. The physics concept of force quantifies the everyday idea of a push or a pull, and like displacement, velocity, and acceleration, force is a vector.
- field
- Physics
- known_for
- Three laws of motion; basis of Newtonian mechanics
- first_stated_by
- Isaac Newton
- published_in
- Philosophiæ Naturalis Principia Mathematica
Lore & Background
Newton's three laws of motion, first presented in Isaac Newton's 1687 work *Philosophiæ Naturalis Principia Mathematica*, form the foundation of classical mechanics. The first law, known as the principle of inertia, states that a body not subject to a net external force will maintain its state of rest or continue moving at a constant speed along a straight line. The second law provides a quantitative relationship: at any given instant, the net force acting on a body equals the product of its mass and its acceleration, which is equivalent to the rate of change of the body's momentum over time. The third law asserts that when two bodies interact, the forces they exert on each other are equal in magnitude and opposite in direction. These laws are typically applied to idealized point masses—bodies whose size is negligible—which is a valid approximation when internal motions are irrelevant and distances between bodies are large relative to their dimensions. The mathematical description of motion, or kinematics, relies on specifying position using numerical coordinates that change over time. Velocity is defined as the derivative of position with respect to time, and acceleration as the derivative of velocity, both being vector quantities with magnitude and direction. Force, like displacement and velocity, is also a vector. Newton's laws successfully explain the motion of many everyday objects and celestial systems, though later developments in quantum mechanics and relativity revealed their limitations in extreme conditions. Concepts such as energy later expanded classical mechanics beyond Newton's original framework.
Reader's Guide
Newton's laws of motion are often stated in terms of point or particle masses, a reasonable approximation for real bodies when the motion of internal parts can be neglected and when the separation between bodies is much larger than the size of each. The mathematical description of motion, or kinematics, is based on specifying positions using numerical coordinates. In the time since Newton, new insights, especially around the concept of energy, built the field of classical mechanics on his foundations. In modern times, limitations to Newton's laws have been discovered; new theories were consequently developed, such as quantum mechanics and relativity to address the physics of objects in more extreme cases.
Did You Know?
- Newton used the laws to investigate and explain the motion of many physical objects and systems.
- In modern times, limitations to Newton's laws have been discovered, leading to new theories such as quantum mechanics and relativity.
- The laws are often stated in terms of point or particle masses, where the body's volume is negligible.
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