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牛顿运动定律

1687

Isaac Newton

A set of three physical laws forming the basis of classical 力学.......。 first law (inertia) states an object remains at rest or in uniform motion unless acted upon by a net external force. The second law quantifies force as mass times acceleration, [latex]\vec{F} = m\vec{a}[/latex]. The third law states that for every action, there is an equal and opposite reaction.

Published in his 1687 work, *Philosophiæ Naturalis Principia Mathematica*, Newton’s three laws of motion revolutionized science. They provided a complete framework for describing the motion of everyday objects, forming the bedrock of what is now known as classical mechanics.

The First Law, the law of inertia, defines an inertial reference frame—a frame of reference where the law holds true. It states that an object’s velocity is constant unless a net force acts upon it. This was a departure from the Aristotelian idea that motion required a continuous force.

The Second Law is the quantitative core of classical dynamics. It states that the net force on an object is equal to the rate of change of its momentum. For an object with constant mass [latex]m[/latex], this simplifies to the famous equation [latex]\vec{F} = m\vec{a}[/latex], where [latex]\vec{F}[/latex] is the net force vector and [latex]\vec{a}[/latex] is the resulting acceleration vector. This is a differential equation, and solving it allows for the prediction of an object’s trajectory through time.

第三定律，即作用力和反作用力定律，指出力总是成对出现的。如果物体A对物体B施加一个力，那么物体B也会同时对物体A施加一个大小相等、方向相反的力。这一原理是理解相互作用的基础，并直接引出了动量守恒定律。

这些定律对于速度远低于光速的宏观世界来说非常精确。但在狭义相对论（高速）和量子力学（原子和亚原子尺度）领域，它们的有效性就被打破了，取而代之的是更普遍的理论。