Momentum and Newton’s Laws | 动量与牛顿定律

📚 Momentum and Newton’s Laws | 动量与牛顿定律

Newton’s laws of motion provide the foundation for understanding how forces change an object’s motion, while linear momentum gives us a powerful conserved quantity for analysing collisions and explosions. In CIE A Level Physics, you need to be able to state the three laws, apply them to systems of interacting bodies, and use momentum conservation in one and two dimensions.

牛顿运动定律为理解力如何改变物体的运动提供了基础，而线性动量则为我们提供了一个强大的守恒量，用于分析碰撞和爆炸。在 CIE A Level 物理中，你需要能够陈述三条定律，将它们应用到相互作用的物体系统，并在一维和二维问题中使用动量守恒。

1. Newton’s First Law | 牛顿第一定律

An object remains at rest or continues to move with constant velocity unless acted upon by a resultant external force. This means that if the vector sum of all forces acting on a body is zero, its velocity does not change.

除非受到合外力的作用，否则物体会保持静止或继续以恒定速度运动。这意味着如果作用在一个物体上的所有力的矢量和为零，它的速度就不会改变。

In exam terms, constant velocity includes both zero velocity and constant speed in a straight line. A common mistake is to think that a moving object needs a forward force to keep moving; in the absence of friction or drag, no net force is needed.

在考试中，恒定速度包括零速度和直线匀速运动两种情况。一个常见错误是认为运动物体需要向前的力才能继续运动；如果没有摩擦或阻力，就不需要净力。

2. Newton’s Second Law | 牛顿第二定律

The resultant force on a body is proportional to its rate of change of momentum. In symbol form:

F = Δp / Δt

作用在物体上的合外力与其动量变化率成正比。用符号表示为 F = Δp / Δt。

For constant mass, this simplifies to F = ma, where a is the acceleration produced. The more general form F = Δp / Δt is especially useful when mass changes, as in rocket motion.

对于质量恒定的情况，这可以简化为 F = ma，其中 a 是产生的加速度。更一般的形式 F = Δp / Δt 在质量变化时尤其有用，例如火箭运动。

Published by TutorHao | A-Level Physics Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）