📚 Conceptual Distinctions in IB & AQA Physics | IB与AQA物理概念辨析
In physics, both IB and AQA syllabuses demand clarity when handling closely related terms. Many marks are lost because students treat speed as velocity, heat as temperature, or momentum as kinetic energy. This article walks through twelve of the most frequently confused concept pairs, providing concise definitions, equations, and examination tips to sharpen your understanding.
在物理中，IB 和 AQA 考纲都要求学生清晰辨析相近术语。很多失分源于学生将速率当作速度、热量当作温度、或动量当作动能。本文梳理十二组最常混淆的概念，给出简明的定义、公式和应试要点，帮助你把概念辨析透彻。
1. Speed vs. Velocity | 速率与速度
Speed is a scalar quantity that tells us how fast an object moves, calculated as total distance divided by time. It never has a direction attached.
速率是标量，表示物体运动的快慢，等于路程除以时间，不涉及方向。
Velocity is a vector quantity equal to displacement divided by time, and therefore includes direction. If a sprinter runs a 400 m lap and returns to the start, the average speed is (400 m)÷(time), but the average velocity is zero because the displacement is zero.
速度是矢量，等于位移除以时间，必然包含方向。若短跑选手跑完一圈 400 米回到起点，平均速率是 400 米除以时间，而平均速度为零，因为位移为零。
average speed = total distance / time
平均速率 = 总路程 / 时间
average velocity = displacement / time
平均速度 = 位移 / 时间
2. Mass vs. Weight | 质量与重量
Mass is a measure of the amount of matter in an object, remains constant regardless of location, and is measured in kilograms (kg).
质量是物体所含物质的多少，无论何处都不变，单位是千克 (kg)。
Weight is the gravitational force acting on a mass, given by W = m × g, and is measured in newtons (N). On Earth, g ≈ 9.8 N kg⁻¹, so a 10 kg object weighs 98 N. On the Moon, g ≈ 1.6 N kg⁻¹, so the same object weighs only 16 N, but its mass is still 10 kg.
重量是作用在质量上的重力，公式 W = m × g，单位是牛顿 (N)。地球上 g ≈ 9.8 N kg⁻¹，一个 10 kg 的物体重 98 N。月球上 g ≈ 1.6 N kg⁻¹，同一物体仅重 16 N，但质量仍为 10 kg。
A balance measures mass by comparing gravitational forces; a spring scale measures weight and would give a different reading on the Moon. In free fall, an object is ‘weightless’ but still possesses mass.
天平通过比较重力来测量质量；弹簧秤测量重量，在月球上读数不同。在自由落体时，物体“失重”但仍具有质量。
W = m g
3. Heat vs. Temperature | 热量与温度
Temperature reflects the average kinetic energy of particles in a substance; it is measured in degrees Celsius (°C) or kelvin (K). A change of 1 °C equals a change of 1 K.
温度反映物质粒子的平均动能，单位是摄氏度 (°C) 或开尔文 (K)。1 °C 的变化等于 1 K 的变化。
Heat is the transfer of thermal energy from a hotter body to a cooler one, measured in joules (J). When heat flows into an object, its temperature may rise, but during a phase change (melting, boiling) the temperature remains constant while latent heat is absorbed.
热量是从高温物体传向低温物体的热能，单位是焦耳 (J)。热流入物体时，它的温度可能上升，但在相变（熔化、沸腾）过程中温度保持不变，同时吸收潜热。
A large iceberg has a low temperature yet contains an enormous amount of heat because of its huge mass. Exam questions often test the distinction by asking about the energy needed to melt ice without temperature change.
一座大冰山温度很低，但因为质量巨大，含有极多的热量。考题常通过询问熔化冰需多少能量而不引起温度变化来检测这一区分。
Q = m c ΔT (sensible heat)
Q = m L (latent heat)
4. Current vs. Voltage | 电流与电压
Electric current (I) is the rate of flow of charge: I = ΔQ / Δt, measured in amperes (A). It is like the flow rate of water through a pipe.
电流 (I) 是电荷流动的速率：I = ΔQ / Δt，单位是安培 (A)。它好比水管中水的流量。
Voltage, or potential difference (V), is the energy transferred per unit charge: V = W / Q, measured in volts (V). It is analogous to the water pressure that drives the flow.
电压，或称电势差 (V)，是每单位电荷转移的能量：V = W / Q，单位是伏特 (V)。它好比驱动水流的水压。
In a series circuit, current is identical everywhere, but the voltage divides across components. In a parallel circuit, the voltage across each branch is the same, while the currents divide. A device will only operate if both current and voltage are supplied appropriately.
串联电路中电流处处相等，但电压在元件上分配。并联电路中各支路电压相等，而电流分流。只有同时提供合适的电流和电压，用电器才能正常工作。
5. Work vs. Energy | 功与能量
Energy is the capacity to do work; it is a stored quantity measured in joules (J) and can exist as kinetic, potential, thermal, or other forms.
能量是做功的本领，是一种储存量，单位是焦耳 (J)，可以表现为动能、势能、热能等形式。
Work is the process of transferring energy when a force causes displacement. It is calculated as the product of the force and the distance moved in the direction of the force: W = F × d × cos θ, where θ is the angle between force and displacement.
功是力引起位移时转移能量的过程。它等于力与沿力方向位移的乘积：W = F × d × cos θ，θ 是力与位移的夹角。
Doing 100 J of work on a box means 100 J of energy is transferred to the box. Power is the rate at which work is done or energy is transferred: P = W / t.
对一个箱子做 100 J 的功，就意味着有 100 J 的能量转移给了箱子。功率是做功或能量转移的速率：P = W / t。
W = F d cos θ
6. Momentum vs. Kinetic Energy | 动量与动能
Momentum (p = m v) is a vector quantity. In the absence of external forces, total momentum is always conserved in collisions, regardless of whether they are elastic or inelastic.
动量 (p = m v) 是矢量。在没有外力时，无论碰撞是弹性还是非弹性，总动量总是守恒。
Kinetic energy (KE = ½ m v²) is a scalar. It is conserved only in perfectly elastic collisions. In inelastic collisions, some kinetic energy is converted into heat, sound, or deformation energy, so total KE decreases.
动能 (KE = ½ m v²) 是标量。它只在完全弹性碰撞中守恒。在非弹性碰撞中，部分动能转化为热、声或形变能，总动能减小。
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