GCSE Physics: Work and Energy – Key Points | GCSE 物理：功与能量 考点精讲

📚 GCSE Physics: Work and Energy – Key Points | GCSE 物理：功与能量 考点精讲

In GCSE Physics, work and energy are core concepts that explain how forces cause movement and how energy is stored, transferred and conserved. Mastering these ideas helps you solve problems involving motion, machines and everyday energy changes. This article covers the essential definitions, equations and worked examples you need to ace your exams.

在GCSE物理中，功和能量是解释力如何引起运动以及能量如何储存、转移和守恒的核心概念。掌握这些概念有助于解决涉及运动、机器和日常能量变化的问题。本文涵盖了考试所需的基本定义、公式以及典型例题。

1. What is Work Done? | 什么是功？

Work is done whenever a force makes something move. In everyday language, ‘work’ can mean any mental or physical effort, but in physics it has a strict meaning – it measures the amount of energy transferred by a force acting over a distance.

当力使物体移动时就做了功。在日常用语中，“工作”可能表示任何脑力或体力劳动，但在物理学中它有严格的定义——它衡量力在作用一段距离时所转移的能量。

If you push against a wall and it does not move, no work is done on the wall because there is no displacement, even though you feel tired. Work requires both a force and movement in the direction of the force.

如果你推墙而墙没有移动，则没有对墙做功，因为位移为零，尽管你会感到疲劳。做功需要同时存在力和沿力方向的移动。

Work done is a scalar quantity measured in joules (J). One joule is equal to one newton-metre (1 J = 1 N m). The formula for work done is straightforward when force and displacement are in the same direction.

功是一个标量，单位是焦耳（J）。1焦耳等于1牛顿·米（1 J = 1 N m）。当力与位移同向时，功的计算公式非常简单。

Work done = force × distance moved in the direction of the force

W = F × d

W is work (J), F is force (N), and d is distance (m). If force is applied at an angle, you must use the component of force parallel to the movement. GCSE usually deals with forces directly along the line of motion.

W 为功（J），F 为力（N），d 为距离（m）。如果力与运动方向有夹角，则需使用沿运动方向的力分量。GCSE阶段通常处理力与运动共线的情况。

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2. Calculating Work Done | 功的计算

In simple situations, you multiply the steady force by the distance the object moves while the force acts. For example, if a gardener pushes a wheelbarrow with a constant force of 80 N over a distance of 5 m, the work done is W = 80 N × 5 m = 400 J.

在简单情况下，可以用恒力的大小乘以物体在力作用期间移动的距离。例如，园丁用80 N的恒力推动独轮车移动5 m，则做功 W = 80 N × 5 m = 400 J。

If a force varies, work can be found from the area under a force-displacement graph, but GCSE papers focus on constant forces. Always check that the distance used is the distance moved in the direction of the force.

如果力是变化的，功可以通过力-位移图像下的面积求得，但GCSE试题集中于恒力。要确保所用的距离是沿力方向移动的距离。

Be careful when forces are perpendicular to motion. If you carry a suitcase while walking horizontally, the upward force you apply does no work on the suitcase because there is no vertical movement. The suitcase does not gain gravitational potential energy horizontally.

当力垂直于运动方向时要当心。如果你水平步行时手提行李箱，你施加的向上的力对行李箱不做功，因为没有竖直方向的移动。行李箱不会因水平移动而获得重力势能。

Conversely, when you lift the suitcase vertically, work is done against gravity, and the work done equals the gravitational potential energy gained.

反之，当你竖直提起行李箱时，克服重力做了功，所做的功等于增加的重力势能。

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3. Gravitational Potential Energy | 重力势能

Gravitational potential energy (GPE) is the energy stored in an object because of its height above a reference point, usually the ground. The higher an object is lifted, the more GPE it stores.

重力势能是物体因其离地高度而储存的能量。物体被抬得越高，储存的重力势能越多。

The equation for GPE is:

重力势能的公式为：

GPE = m × g × h

where m is mass in kilograms (kg), g is gravitational field strength in newtons per kilogram (N/kg), and h is vertical height in metres (m). On Earth, g is about 9.8 N/kg, but exams often use 10 N/kg for simplicity.

其中 m 为质量（kg），g 为重力场强度（N/kg），h 为竖直高度（m）。在地球上 g 约为 9.8 N/kg，考试中常简化为 10 N/kg。

For example, a 2 kg book lifted onto a shelf 1.5 m high gains GPE = 2 kg × 10 N/kg × 1.5 m = 30 J. That energy originally came from the person lifting the book, who did 30 J of work.

例如，一本 2 kg 的书被抬到 1.5 m 高的书架上，获得的重力势能为 GPE = 2 kg × 10 N/kg × 1.5 m = 30 J。这份能量来自抬书的人，他做了 30 J 的功。

When an object falls freely, its GPE decreases as it converts into kinetic energy, assuming no air resistance. This conversion is a key example of the conservation of energy.

当物体自由下落时，其重力势能减少，转化为动能，假设没有空气阻力。这种转化是能量守恒的一个重要实例。

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4. Kinetic Energy | 动能

Kinetic energy (KE) is the energy an object possesses due to its motion. Any moving object – a rolling ball, a flying arrow, a spinning wheel – has kinetic energy.

动能是物体由于运动而具有的能量。任何运动的物体——滚动的球、飞行的箭、旋转的车轮——都具有动能。

The kinetic energy equation is:

动能公式为：

KE = ½ × m × v²

m is mass (kg) and v is speed in metres per second (m/s). Because speed is squared, a small increase in speed causes a large increase in KE. Doubling the speed makes the kinetic energy four times greater.

m 为质量（kg），v 为速度（m/s）。由于速度是平方项，速度的小幅增加会导致动能大幅增加。速度加倍，动能变为原来的四倍。

This relationship explains why high-speed collisions are far more dangerous. A car travelling at 60 mph has four times the kinetic energy of the same car at 30 mph, not twice.

这个关系解释了为何高速碰撞危险得多。一辆以 60 mph 行驶的汽车所具有的动能是同一辆车以 30 mph 行驶时的四倍，而不是两倍。

Kinetic energy is measured in joules (J). When a car brakes, friction converts its kinetic energy into thermal energy in the brakes and tyres, slowing it down.

动能以焦耳（J）为单位。汽车刹车时，摩擦力将其动能转化为刹车和轮胎中的热能，从而减速。

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5. Elastic Potential Energy | 弹性势能

Elastic potential energy (EPE) is stored in objects that can be stretched or compressed, such as springs, elastic bands, and bungee cords. This energy is released when the object returns to its original shape.

弹性势能储存在可拉伸或压缩的物体中，如弹簧、橡皮筋和蹦极绳。当物体恢复原状时，这部分能量会被释放。

The formula for elastic potential energy, within the elastic limit, is:

在弹性限度内，弹性势能的公式为：

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