Forces and Motion | 力与运动

📚 Forces and Motion | 力与运动

In your Edexcel IGCSE Science course, the topic of forces and motion is the bridge between physics and the world around you. From a sprinter accelerating off the blocks to a parachutist reaching terminal velocity, the same ideas apply: distance, speed, acceleration, mass, weight and forces. In this revision guide, you will learn the definitions you must quote, the equations you must be able to rearrange, and the graph skills you must master to score full marks in your exam.

在爱德思 IGCSE 科学课程中，力与运动这一主题是连接物理与周围世界的桥梁。从短跑运动员蹬离起跑器加速，到跳伞者达到收尾速度，相同的概念始终适用：距离、速率、加速度、质量、重量和力。在本复习指南中，你将学习必须引用的定义、必须会变形的方程，以及必须在考试中拿满分的读图技巧。

1. Distance, Displacement, Scalar and Vector Quantities | 距离、位移、标量与矢量

Distance is the total length of the path that an object actually travels, measured along the route it takes. Displacement is the straight-line distance from an object’s starting position to its finishing position, together with the direction. For example, if a runner completes one lap of a 400 m track, the distance travelled is 400 m, but the displacement at the end is zero because the runner is back at the start.

距离是物体实际运动所经过路径的总长度。位移是从物体的起点到终点的直线距离，并且要指明方向。例如，若一名跑步者沿 400 m 跑道跑完一圈，则其路程距离为 400 m，但最终位移为零，因为跑步者回到了起点。

This difference matters because distance is a scalar quantity, which has size (magnitude) only, while displacement is a vector quantity, which has both magnitude and direction. Speed is the scalar twin of velocity; time, mass and temperature are also scalars. Force, velocity and acceleration are vectors.

这一区别很重要，因为距离是标量，只有大小；而位移是矢量，既有大小又有方向。速率是速度的标量“姊妹量”；时间、质量和温度也是标量。力、速度和加速度都是矢量。