IB & CIE Physics: Common Mistake Questions Explained | IB CIE 物理：易错题精讲

📚 IB & CIE Physics: Common Mistake Questions Explained | IB CIE 物理：易错题精讲

In IB and CIE Physics, even strong students often lose marks on seemingly straightforward questions due to subtle conceptual misunderstandings or sign errors. This article dissects ten classic mistake-prone topics, providing clear explanations and correct reasoning to help you avoid common pitfalls in your exams.

在IB和CIE物理考试中，许多同学常因为细微的概念混淆或符号错误而在简单题上失分。本文剖析了十个经典的易错知识点，并给出清晰的解析和正确思路，帮助你在考试中避开常见陷阱。

1. Displacement vs Distance Confusion | 位移与路程混淆

Many students incorrectly equate distance travelled with the magnitude of displacement. Consider a particle that moves along a semicircular path of radius r from point A to point B at the opposite end of the diameter. The total path length (distance) is half the circumference: πr. However, displacement is the straight-line vector from start to finish, with magnitude equal to the diameter 2r, directed from A to B. A typical mistake is to answer ‘πr’ for displacement. For example, if r = 5.0 m, the distance is 15.7 m but the displacement is 10.0 m towards B. Always remember: distance is a scalar and depends on the path taken, while displacement is a vector determined solely by the initial and final positions.

很多学生错误地将路程等同于位移的大小。设想一个质点沿半径为r的半圆弧从A点运动到直径另一端的B点。总路径长度（路程）为半周长πr。然而，位移是从起点指向终点的直线向量，大小为直径2r，方向由A指向B。典型的错误是直接用πr回答位移。例如，若r=5.0 m，路程为15.7 m，位移却是10.0 m指向B。务必牢记：路程是标量，取决于路径；位移是矢量，仅由初末位置决定。

2. Misapplying Newton’s Third Law | 错用牛顿第三定律

A classic error is identifying the weight of a book resting on a table and the normal force from the table as an action–reaction pair. Although they are equal in magnitude and opposite in direction, they act on the same object (the book), so they cannot be a third-law pair. Newton’s third law requires forces to act on two different bodies. The correct reaction to the book’s weight is the gravitational force exerted by the book on the Earth; the reaction to the normal force is the downward force the book exerts on the table. Grasping this distinction is crucial for free-body diagrams and for understanding why balanced forces do not automatically form a third-law pair.

一个经典错误是把静止在桌面上的书所受的重力与桌面对书的支持力看作一对作用力与

Published by TutorHao | IB Physics Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）