A-Level CCEA Science: Energy – Key Points Revision | 能量考点精讲

📚 A-Level CCEA Science: Energy – Key Points Revision | 能量考点精讲

Energy is one of the most fundamental and unifying concepts in science, spanning physics, chemistry, and biology. In CCEA A-Level Science, particularly in the Physics modules, a thorough understanding of energy forms, transfers, conservation, and calculations is essential for exam success. This revision guide covers the key definitions, formulas, and problem-solving techniques you need to master energy topics at AS and A2 level.

能量是科学中最基本、最统一的概念之一，贯穿物理、化学和生物学。在 CCEA A-Level 科学课程中，尤其是物理模块，透彻理解能量的形式、转化、守恒以及相关计算对于考试成功至关重要。本复习指南涵盖你在 AS 和 A2 阶段需要掌握的能量主题的关键定义、公式和解题技巧。

1. Work Done by a Force | 力做的功

Work is done when a force moves an object through a distance. The work done W by a constant force F acting on an object that moves a displacement s is given by W = F s cos θ, where θ is the angle between the force and the displacement. The SI unit of work is the joule (J). If the force is parallel to the displacement (θ = 0°), work is simply W = F s. When the force is perpendicular to the displacement (θ = 90°), no work is done, because cos 90° = 0.

当一个力使物体移动一段距离时，该力对物体做了功。恒力 F 作用在物体上，使其发生位移 s，所做的功 W 由公式 W = F s cos θ 给出，其中 θ 是力与位移之间的夹角。功的国际单位是焦耳（J）。如果力与位移方向平行（θ = 0°），则功简化为 W = F s。当力垂直于位移（θ = 90°）时，不做功，因为 cos 90° = 0。

W = F s cos θ

It is important to note that work is a scalar quantity, but it can be positive or negative. Positive work increases the energy of the object, while negative work (e.g., friction) decreases its energy.

需要特别注意的是，功是标量，但有正负之分。正功增加物体的能量，而负功（如摩擦力做功）则减少物体的能量。

• Positive work: force component in direction of motion → energy increases.
• 正功：力的分量与运动方向相同 → 能量增加。
• Negative work: force component opposite to motion → energy decreases.
• 负功：力的分量与运动方向相反 → 能量减少。
• Zero work: force perpendicular to displacement, or no displacement.
• 零功：力垂直于位移，或无位移发生。

2. Kinetic Energy | 动能

Kinetic energy is the energy an object possesses due to its motion. For an object of mass m moving with speed v, its translational kinetic energy E_k is given by E_k = ½ m v². This relationship shows that kinetic energy is directly proportional to the mass and to the square of the speed. Thus, doubling the speed quadruples the kinetic energy.

动能是物体由于运动而具有的能量。对于质量为

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