📚 KS3 CIE Forces 1: Year 7 Scheme of Work | KS3 CIE 力 1：七年级教学计划
This scheme of work supports Year 7 students following the Cambridge Lower Secondary Science (CIE KS3) curriculum for the topic 'Forces 1'. It breaks the topic into clear learning objectives, key ideas, practical activities and common misconceptions so teachers can plan a coherent sequence of lessons. Students will explore what forces do, how to measure them, and how balanced and unbalanced forces explain everyday motion.
本教学计划面向学习剑桥初中科学（CIE KS3）课程“力 1”专题的七年级学生。它把该专题拆分为清晰的学习目标、核心概念、实践活动和常见误区，帮助教师规划连贯的课程序列。学生将探索力的作用、如何测量力，以及平衡与不平衡力如何解释日常运动。
1. What is a Force? | 什么是力？
A force is a push or a pull acting on an object. Forces cannot be seen, but their effects can be observed: they can change the speed of an object, change its direction, or change its shape. The unit of force is the newton (N), named after Sir Isaac Newton.
力是作用在物体上的推或拉。力本身看不见，但它的作用可以被观察到：力可以改变物体的速度、改变其运动方向或改变其形状。力的单位是牛顿（N），以艾萨克·牛顿爵士的名字命名。
Forces always occur in pairs when two objects interact. For example, when you kick a ball, your foot applies a force to the ball, and the ball applies an equal and opposite force to your foot.
当两个物体相互作用时，力总是成对出现。例如，当你踢球时，你的脚对球施加一个力，球也对你的脚施加一个大小相等、方向相反的力。
In Year 7, students learn to identify forces in familiar situations such as pushing a trolley, stretching a rubber band, dropping a ball and sitting on a chair.
在七年级，学生要学会识别熟悉情境中的力，例如推手推车、拉伸橡皮筋、扔下球和坐在椅子上。
2. Types of Forces | 力的类型
Forces can be divided into two main groups: contact forces and non-contact forces. Contact forces require objects to touch each other, while non-contact forces act at a distance.
力可分为两大类：接触力和非接触力。接触力需要物体相互接触，而非接触力可以在一定距离外产生作用。
Common contact forces include friction, air resistance, water resistance, tension and the normal reaction force. Common non-contact forces include gravity, magnetic force and electrostatic force.
常见的接触力包括摩擦力、空气阻力、水的阻力、张力和法向反作用力。常见的非接触力包括重力、磁力和静电力。
A useful classroom activity is to sort pictures of everyday actions into contact and non-contact force examples. This helps students see that gravity acts without touching, while friction only appears when surfaces rub together.
一个有用的课堂活动是将日常动作的图片分为接触力和非接触力两类。这有助于学生明白重力不接触就能起作用，而摩擦力只有在表面相互摩擦时才会出现。
| Contact forces | Non-contact forces |
|---|---|
| Friction | Gravity |
| Air resistance | Magnetic force |
| Tension | Electrostatic force |
3. Measuring Forces | 测量力
Forces are measured with a newton meter, also called a spring balance or force meter. The reading is taken in newtons (N). A newton meter works by measuring the extension of a spring: the greater the force, the more the spring stretches.
力用牛顿计测量，也称为弹簧秤或测力计。读数以牛顿（N）为单位。牛顿计通过测量弹簧的伸长来工作：力越大，弹簧拉伸得越长。
In the laboratory, students can practise measuring forces by pulling objects across different surfaces, hanging masses from a newton meter, or stretching elastic bands. The key skill is reading the scale correctly and aligning the eye with the pointer to avoid parallax error.
在实验室中，学生可以通过在不同表面上拉动物体、在牛顿计上悬挂砝码或拉伸橡皮筋来练习测量力。关键技能是正确读取刻度，并让视线与指针对齐以避免视差误差。
When measuring weight, the newton meter should be held vertically. When measuring a horizontal pull, it should be held parallel to the direction of motion.
测量重量时，牛顿计应竖直握住。测量水平拉力时，应使其与运动方向平行。
4. Representing Forces with Arrows | 用箭头表示力
Forces are drawn as arrows on force diagrams. The length of the arrow shows the size (magnitude) of the force, the direction of the arrow shows the direction of the force, and the starting point shows where the force acts.
力在力的示意图中用箭头表示。箭头的长度表示力的大小（大小），箭头方向表示力的方向，起点表示力的作用点。
For example, an object resting on a table has a downward weight arrow and an upward normal reaction arrow of equal length. A moving car being pushed has a longer thrust arrow pointing forward and a shorter friction arrow pointing backward.
例如，放在桌子上的物体有一个向下的重力箭头和一个向上的法向反作用力箭头，两者长度相等。一辆被推动的汽车有一个向前的较长推力箭头和一个向后的较短摩擦力箭头。
bels and a scale, such as 1 cm = 1 N. This prepares them for calculating resultant forces.
学生应练习绘制带清晰标注和比例（如 1 厘米 = 1 牛）的简单受力图。这为他们计算合力做好准备。
5. Balanced and Unbalanced Forces | 平衡力与不平衡力
When all forces acting on an object are balanced, the resultant force is zero. The object either stays still or continues moving at a constant speed in a straight line. This is a simple statement of Newton's first law of motion.
当作用在物体上的所有力相互平衡时，合力为零。物体要么保持静止，要么继续沿直线匀速运动。这是牛顿第一运动定律的简单表述。
When forces are unbalanced, the resultant force is not zero. The object will speed up, slow down or change direction. The acceleration is in the direction of the resultant force.
当力不平衡时，合力不为零。物体将加速、减速或改变方向。加速度的方向与合力的方向一致。
A common experiment uses a wooden block pulled by a newton meter. When the pull is small and the block does not move, friction is equal and opposite to the pull, so forces are balanced. When the pull becomes large enough, the block moves and forces become unbalanced.
一个常见实验是用牛顿计拉木块。当拉力较小、木块不动时，摩擦力与拉力大小相等、方向相反，因此力是平衡的。当拉力足够大时，木块开始运动，力变得不平衡。
Resultant force = forward force - backward force
6. Friction | 摩擦力
Friction is a contact force that opposes motion between two surfaces that are sliding or trying to slide past each other. It is caused by microscopic roughness on the surfaces.
摩擦力是一种接触力，它阻碍两个相互滑动或试图相互滑动的表面之间的运动。它是由表面上的微观粗糙引起的。
Friction can be useful or unwanted. Useful friction allows us to walk without slipping, stops cars safely and lets us hold objects. Unwanted friction wears out machine parts and wastes energy as heat.
摩擦力可能是有益的，也可能是有害的。有益摩擦使我们走路不打滑、让汽车安全停下、让我们能握住物体。有害摩擦会磨损机器零件并以热的形式浪费能量。
Friction can be reduced by using lubricants such as oil or grease, by smoothing surfaces, or by using wheels and ball bearings. It can be increased by making surfaces rougher or pressing them together harder.
摩擦可以通过使用油或油脂等润滑剂、打磨光滑表面或使用轮子和滚珠轴承来减小。可以通过使表面更粗糙或更用力地挤压表面来
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