KS3 CIE Moments Exam Question and Mark Scheme | KS3 CIE 力矩考试题与评分方案

📚 KS3 CIE Moments Exam Question and Mark Scheme | KS3 CIE 力矩考试题与评分方案

This article breaks down a typical KS3 CIE-style moment question and its mark scheme. You will learn how examiners award marks for definitions, calculations, and explanations, and how to avoid the most common errors.

本文解析一道典型的 KS3 CIE 风格力矩考题及其评分方案。你将了解考官如何对定义、计算和解释分配分数，以及如何避免最常见的错误。

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1. What Is a Moment? | 什么是力矩

A moment is the turning effect of a force acting about a pivot. It is measured in newton metres (N m).

力矩是力绕支点产生的转动效应。它的单位是牛顿米（N m）。

The size of a moment depends on two things: the size of the force and the perpendicular distance from the pivot to the line of action of the force.

力矩的大小取决于两个因素：力的大小，以及从支点到力的作用线的垂直距离。

In everyday life, moments are used when you push a door handle, use a spanner to turn a nut, or sit on a see-saw.

在日常生活中，当你推门把手、用扳手转动螺母或坐在跷跷板上时，都会用到力矩。

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2. The Moment Equation | 力矩公式

The moment equation is:

力矩公式为：

M = F × d

where M is the moment in newton metres (N m), F is the force in newtons (N), and d is the perpendicular distance from the pivot in metres (m).

其中 M 是力矩，单位为牛顿米（N m）；F 是力，单位为牛顿（N）；d 是从支点开始测量的垂直距离，单位为米（m）。

The equation can be rearranged to find force or distance:

公式可以变形以求解力或距离：

F = M ÷ d

d = M ÷ F

This is useful when a question gives the moment and one other quantity.

当题目给出力矩和另一个量时，这很有用。

Always check that the distance is perpendicular to the force. If the force is not at 90° to the lever, you must use the perpendicular component of the distance.

务必检查距离是否与力垂直。如果力与杠杆不成 90°，则必须使用距离的垂直分量。

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3. The Principle of Moments | 力矩原理

The principle of moments states that for an object in equilibrium, the sum of the clockwise moments about any pivot is equal to the sum of the anticlockwise moments about that pivot.

力矩原理指出：对于处于平衡状态的物体，绕任意支点的顺时针力矩之和等于逆时针力矩之和。

This is often written as:

这通常写作：

total clockwise moments = total anticlockwise moments

N × 0.4 m = 0.8 N m. To balance it, a clockwise moment of 0.8 N m is needed on the right.

例如，如果一个 2 N 的力作用在支点左侧 0.4 m 处，其逆时针力矩为 2 N × 0.4 m = 0.8 N m。为了平衡，右侧需要 0.8 N m 的顺时针力矩。

In KS3 CIE questions, you will usually apply this to a balanced see-saw or a simple lever.

在 KS3 CIE 考试中，你通常要将这一原理应用于平衡的跷跷板或简单杠杆。

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4. The Exam Question | 考试题目

Below is a typical KS3 CIE-style question. Read each part carefully before looking at the mark scheme.

下面是一道典型的 KS3 CIE 风格考题。在查看评分方案之前，请仔细阅读每一部分。

Question:

题目：

A uniform metre rule is pivoted at its centre. A 2.0 N weight is hung 0.30 m from the pivot on the left-hand side.

一把均匀的米尺在其中点被支起。一个 2.0 N 的砝码挂在支点左侧 0.30 m 处。

(a) State what is meant by the moment of a force. [2]

(a) 说明力的力矩是什么意思。[2 分]

(b) Calculate the moment of the 2.0 N weight about the pivot. Give the unit. [2]

(b) 计算 2.0 N 砝码绕支点的力矩。写出单位。[2 分]

(c) A second weight is hung on the right-hand side of the pivot to balance the rule. Describe how you would find the position of this weight using the principle of moments. [4]

(c) 在支点右侧挂上第二个砝码使米尺平衡。描述你如何利用力矩原理找到该砝码的位置。[4 分]

(d) The second weight is 4.0 N. Calculate the distance from the pivot at which it must be hung. [2]

(d) 第二个砝码为 4.0 N。计算它必须挂在距离支点多远处。[2 分]

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5. Part (a): Defining a Moment | 小题 (a)：定义力矩

For part (a), a full mark answer should mention two key ideas: turning effect and force.

对于小题 (a)，满分答案应包含两个关键点：转动效应和力。

A model answer is: 'A moment is the turning effect of a force about a pivot.'

标准答案是：“力矩是力绕支点产生的转动效应。”

The mark scheme often gives 1 mark for 'turning effect' and 1 mark for 'force about a pivot'.

评分方案通常为“转动效应”给 1 分，“力绕支点”给 1 分。

Some mark schemes also accept 'the product of force and perpendicular distance from the pivot'.

有些评分方案也接受“力与从支点

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