📚 Year 8 Edexcel Science: Quick Reference Handbook of Formulas and Theorems | Year 8 Edexcel 科学：公式定理速查手册
Welcome to your one-stop quick reference for Year 8 Edexcel Science. This handbook pulls together the must-know formulas and principles from physics, chemistry and biology that you will encounter in your lessons, homework and assessments. Each section presents the key equation, explains what the symbols mean and shows you how to apply the ideas. Keep it close for last-minute revision or as a daily study companion.
欢迎使用你的 Year 8 Edexcel 科学一站式速查手册。本手册汇集了你在物理、化学和生物课堂、作业和测评中一定会碰到的核心公式和原理。每个小节都给出了关键方程，解释了符号含义，并展示了如何运用这些思想。平时翻阅或考前速查都十分方便。
1. Speed (Distance-Time) | 速度（距离-时间）
Speed describes how fast an object is moving without regard to direction. It tells you the distance covered in a certain amount of time and is one of the most fundamental quantities in motion.
速度描述物体移动的快慢，不考虑方向。它告诉你在一段时间内通过的距离，是运动学中最基本的物理量之一。
To calculate average speed, you divide the total distance travelled by the time taken.
要计算平均速度，用总路程除以所花时间。
speed = distance ÷ time
v = d ÷ t
tance and seconds (s) for time. Sometimes you will also see kilometres per hour (km/h); you can convert by remembering 1 m/s = 3.6 km/h.
公式中 v 代表速度，d 表示距离，t 是时间。标准国际单位是米每秒（m/s）表示速度，米（m）表示距离，秒（s）表示时间。有时候你也会看到千米每小时（km/h）；换算时记住 1 m/s = 3.6 km/h。
You can use the formula triangle: cover the symbol you want to solve for. If you need distance, multiply speed by time. If you need time, divide distance by speed.
你可以使用公式三角形：遮住你想要求解的字母。如果需要距离，速度乘以时间；如果需要时间，距离除以速度。
2. Acceleration | 加速度
Acceleration is the rate at which an object's velocity changes. Velocity is speed in a given direction, so acceleration can involve speeding up, slowing down or changing direction.
加速度是物体速度变化的快慢。速度是带有方向的速率，因此加速度可以包括加速、减速或者改变方向。
acceleration = (final velocity − initial velocity) ÷ time
a = (v − u) ÷ t
Here a stands for acceleration, v is final velocity, u is initial velocity and t is the time taken for the change. The unit of acceleration is metres per second squared (m/s²). A negative acceleration means the object is decelerating.
这里 a 代表加速度，v 是末速度，u 是初速度，t 是变化所用的时间。加速度的单位是米每二次方秒（m/s²）。负的加速度表示物体正在减速。
For a constant acceleration, the change in velocity is steady. A steeper gradient on a velocity-time graph indicates a greater acceleration.
对于匀加速，速度的变化是均匀的。在速度-时间图上，斜率越大表示加速度越大。
3. Force, Mass and Weight | 力、质量与重量
A force is a push or a pull that can change an object's shape, speed or direction. The unit of force is the newton (N). The mass of an object tells you how much matter it contains and is measured in kilograms (kg).
力是一种推或拉，能改变物体的形状、速度或方向。力的单位是牛顿（N）。物体的质量告诉你它含有多少物质，以千克（kg）为单位。
Weight is not the same as mass. Weight is the force of gravity acting on an object and depends on the gravitational field strength.
重量不等于质量。重量是作用在物体上的重力，取决于引力场强度。
weight = mass × gravitational field strength
W = m × g
On Earth, the gravitational field strength g is approximately 10 N/kg (more precisely 9.8 N/kg). So a 1 kg mass has a weight of about 10 N. Mass is constant everywhere; weight changes if you go to the Moon because g is smaller there.
在地球上，引力场强度 g 大约为 10 N/kg（更精确为 9.8 N/kg）。因此 1 kg 的物体重量约为 10 N。质量各处不变；如果你去到月球，因为那里的 g 更小，重量会发生变化。
4. Pressure | 压强
Pressure measures how concentrated a force is over a surface. A large force applied over a small area produces a high pressure.
压强测量力在一个表面上的集中程度。较大的力作用在较小面积上会产生较高的压强。
pressure = force ÷ area
P = F ÷ A
ease pressure by increasing the force or decreasing the area. That is why a sharp knife cuts more easily than a blunt one: the same force is spread over a much smaller area.
压强的单位是帕斯卡（Pa），1 Pa = 1 N/m²;。你可以通过增大压力或减小面积来增大压强。这就是为什么锋利的刀比钝刀更容易切割：同样的力分布在更小的面积上。
If you need to reduce pressure (e.g. to stop sinking into soft ground), you increase the area, such as by wearing snowshoes.
如果需要减小压强（例如防止陷入松软地面），你可以增大面积，比如穿上雪鞋。
5. Density | 密度
Density is a measure of how much mass is packed into a given volume. It helps to explain why some objects float while others sink.
密度衡量单位体积内含有多少质量。它能帮助解释为什么有些物体漂浮而有些下沉。
density = mass ÷ volume
ρ = m ÷ V
Density is often expressed in kilograms per cubic metre (kg/m³) or grams per cubic centimetre (g/cm³). The Greek letter ρ (rho) is the symbol for density. Water has a density of about 1 g/cm³ or 1000 kg/m³.
密度通常以千克每立方米（kg/m³）或克每立方厘米（g/cm³）表示。希腊字母 ρ 是密度的符号。水的密度大约为 1 g/cm³ 或 1000 kg/m³。
An object will float if its density is less than the density of the fluid it is placed in. It sinks if its density is greater.
如果物体的密度小于它所在流体的密度，它就会漂浮；如果它的密度更大，则下沉。
6. Work, Energy and Power | 功、能量与功率
Work is done whenever a force moves an object in the direction of the force. Energy is the ability to do work, both measured in joules (J).
每当一个力使物体沿力的方向移动时，力就做了功。能量是做功的本领，两者单位都是焦耳（J）。
work done = force × distance moved in the direction of the force
W = F × d
rk is done or energy is transferred. The unit of power is the watt (W), where 1 W = 1 J/s.
功率是做功或能量转移的速率。功率的单位是瓦特（W），1 W = 1 J/s。
power = work done ÷ time
P = W ÷ t
Energy can change from one form to another, but the total amount of energy in a closed system stays constant. This is the principle of conservation of energy.
能量可以从一种形式转化为另一种形式，但在一个封闭系统中，能量的总量保持不变。这就是能量守恒原理。
7. Gravitational Potential and Kinetic Energy | 重力势能与动能
Gravitational potential energy (GPE) is stored in an object because of its height above the ground. The higher it is lifted, the more GPE it gains.
重力势能（GPE）储存在物体中是由于它离地面的高度。物体被举得越高，获得的重力势能就越多。
GPE = mass × gravitational field strength × height
GPE = m × g × h
Kinetic energy (KE) is the energy an object possesses due to its motion. A faster or heavier object has more kinetic energy.
动能（KE）是物体由于运动而具有的能量。物体越快、越重，动能就越大。
KE = ½ × mass × velocity²
KE = ½ × m × v²
When an object falls, GPE is converted into KE, assuming no air resistance. The sum of GPE and KE (mechanical energy) stays the same if only gravity does work.
当物体下落（忽略空气阻力）时，重力势能转化为动能。若只有重力做功，GPE 与 KE 的总和（机械能）保持不变。
8. Hooke's Law and Elastic Potential Energy | 胡克定律与弹性势能
Many springs and elastic objects obey Hooke's Law up to a certain limit. This law states that the extension of a spring is directly proportional to the force applied, provided the elastic limit is not exceeded.
许多弹簧和弹性物体在一定限度内遵循胡克定律。该定律指出，弹簧的伸长量与施加的力成正比，前提是不超过弹性限度。
force = spring constant × extension
F = k × e
The spring constant k is measured in newtons per metre (N/m) and tells you how stiff the spring is. A stiffer spring has a larger k.
弹簧常数 k 的单位是牛每米（N/m），它表示弹簧的刚度。刚度越大的弹簧 k 值越大。
Work is stored as elastic potential energy in a stretched or compressed spring. The energy stored can be found using:
功被储存为拉伸或压缩弹簧的弹性势能。储存的能量可以用下式求出：
elastic potential energy = ½ × spring constant × extension²
E = ½ × k × e²
If you stretch the spring beyond its elastic limit, it becomes permanently deformed and Hooke's Law no longer applies.
如果拉伸超过弹性限度，弹簧就会发生永久变形，胡克定律不再适用。
9. Electricity: Ohm's Law | 电学：欧姆定律
Ohm's Law links the current flowing through a conductor, the voltage across it and its resistance. It holds true for many components at constant temperature.
欧姆定律将流过导体的电流、导体两端的电压和电阻联系起来。对于在恒温下的许多元件，该定律成立。
voltage = current × resistance
V = I × R
Voltage (V) is measured in volts (V), current (I) in amperes (A) and resistance (R) in ohms (Ω). A larger resistance reduces the current for a given voltage.
电压（V）以伏特（V）为单位，电流（I）以安培（A）为单位，电阻（R）以欧姆（Ω）为单位。在给定电压下，电阻越大电流越小。
rmula using a triangle: cover the unknown quantity. I = V ÷ R and R = V ÷ I.
你可以用三角形来变换公式：遮住未知量。I = V ÷ R，R = V ÷ I。
10. Moments (Torque) | 力矩
A moment is the turning effect of a force. It depends on the size of the force and the perpendicular distance from the pivot to the line of action of the force.
力矩是力产生的转动效应。它取决于力的大小以及从支点到力的作用线的垂直距离。
moment = force × perpendicular distance from pivot
M = F × d
The unit of a moment is newton-metre (Nm). To achieve balance on a see-saw, the total clockwise moment must equal the total anticlockwise moment about the pivot.
力矩的单位是牛·米（Nm）。要使跷跷板平衡，顺时针方向的总力矩必须等于逆时针方向的总力矩（相对于支点）。
You can increase a moment by applying a larger force or by pushing further from the pivot. That is why a door handle is placed far from the hinges.
增大力矩的方法是施加
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