📚 Year 7 OCR Physics: Formula and Theorem Quick Reference Handbook | Year 7 OCR 物理：公式定理速查手册
This handbook brings together the essential formulas, equations and key principles you need for Year 7 OCR Physics. Use it as a rapid reference when solving problems, revising for tests or checking your understanding of how the physical world works. Each section pairs a clear explanation with a memorable formula, followed by the quantities and units involved.
这份速查手册汇总了 Year 7 OCR 物理课程中你必须掌握的核心公式、方程和重要原理。你可以在解题、复习备考或检验自己对物理世界的理解时快速查阅。每个小节都配有清晰的解释和易记的公式，并标明了各个物理量及其单位。
1. Speed, Distance and Time | 速度、距离和时间
Speed tells us how fast an object is moving. It is the distance travelled in a certain amount of time. The average speed can be found by dividing the total distance by the total time taken. If an object moves at a steady speed, the same formula applies.
速度告诉我们物体运动的快慢。它是物体在一定时间内通过的距离。平均速度可以用总距离除以总时间求得。如果物体保持匀速运动，使用的公式是相同的。
average speed = total distance ÷ total time
v = d ÷ t
| Symbol | Quantity | SI unit |
|---|---|---|
| v (or s) | speed | metres per second (m/s) |
| d | distance | metres (m) |
| t | time | seconds (s) |
You can rearrange the equation to find distance (d = v × t) or time (t = d ÷ v). Always check that the units match: if distance is in metres and time in seconds, speed comes out in m/s. If you have kilometres and hours, speed will be in km/h.
你可以通过公式变形求出距离（d = v × t）或时间（t = d ÷ v）。务必确保单位统一：如果距离用米、时间用秒，那么速度的单位就是米/秒（m/s）。如果路程用千米、时间用小时，速度单位就是千米/小时（km/h）。
2. Weight and Mass | 重量和质量
Mass is the amount of matter in an object and is measured in kilograms (kg). Weight is the force of gravity pulling on that mass. Weight and mass are related by the gravitational field strength, g. On Earth, g ≈ 10 N/kg (or more precisely 9.8 N/kg).
质量是物体所含物质的多少，单位是千克（kg）。重量是作用在该质量上的重力。重量和质量通过重力场强度 g 相联系。在地球表面，g 约等于 10 N/kg（更精确的值为 9.8 N/kg）。
weight = mass × gravitational field strength
W = m × g
| Symbol | Quantity | Unit |
|---|---|---|
| W | weight | newtons (N) |
| m | mass | kilograms (kg) |
| g | gravitational field strength | newtons per kilogram (N/kg) |
Remember: mass does not change when you go to the Moon, but your weight does because the Moon has a smaller g (about 1.6 N/kg). The weight force always points downwards towards the centre of the Earth.
注意：即使到了月球，质量也不会改变，但重量会变化，因为月球的重力场强度 g 较小（约 1.6 N/kg）。重力的方向总是竖直向下指向地球中心。
3. Density | 密度
Density measures how tightly packed the matter is inside a substance. It is the mass per unit volume. Solids generally have higher densities than liquids and gases because their particles are closer together.
密度表示物质内部质量的密集程度，定义为单位体积的质量。固体通常比液体和气体具有更高的密度，因为固体的微粒排列得更紧密。
density = mass ÷ volume
ρ = m ÷ V
| Symbol | Quantity | Unit |
|---|---|---|
| ρ (rho) | density | kilograms per metre cubed (kg/m³) |
| m | mass | kilograms (kg) |
| V | volume | metres cubed (m³) or cm³ |
Density can also be expressed in grams per centimetre cubed (g/cm³). To convert from kg/m³ to g/cm³, divide by 1000. Water has a density of exactly 1000 kg/m³ (or 1 g/cm³). An object floats if its density is less than the density of the fluid it is placed in.
密度也可以用克每立方厘米（g/cm³）表示。由 kg/m³ 换算为 g/cm³ 只需除以 1000。水的密度恰好是 1000 kg/m³（即 1 g/cm³）。如果物体的密度小于它所在液体的密度，物体就会漂浮。
4. Pressure | 压强
Pressure describes how concentrated a force is over an area. When the same force is applied over a smaller area, the pressure increases. This principle explains why sharp knives cut more easily and why snow shoes stop you sinking into snow.
压强描述的是力作用于某一面积时的集中程度。在同样的力作用下，受力面积越小，压强越大。这就是为什么锋利的刀更容易切割，以及雪地靴防止你陷入雪中的原理。
pressure = force ÷ area
P = F ÷ A
| Symbol | Quantity | Unit |
|---|---|---|
| P | pressure | pascals (Pa) or N/m² |
| F | force | newtons (N) |
| A | area | square metres (m²) |
1 pascal means a force of 1 newton acting on an area of 1 m². In liquids and gases, pressure acts in all directions and increases with depth. This is called fluid pressure.
1 帕斯卡（Pa）表示 1 牛顿的力作用在 1 平方米的面积上。在液体和气体中，压强向各个方向作用，并且随着深度增加而增大，这叫做流体压强。
5. Hooke’s Law | 胡克定律
When you stretch a spring by adding weights, the extension increases steadily with the load – as long as you do not over-stretch the spring. Robert Hooke discovered that the extension of a spring is directly proportional to the force applied, provided the elastic limit is not exceeded.
当你通过增加砝码来拉长弹簧时，只要不过度拉伸，弹簧的伸长量会随着载荷的增加而均匀增大。罗伯特·胡克发现：在不超过弹性极限的前提下，弹簧的伸长量与施加的力成正比。
force ∝ extension (F ∝ e)
F = k × e
| Symbol | Quantity | Unit |
|---|---|---|
| F | applied force | newtons (N) |
| e | extension (change in length) | metres (m) or cm |
| k | spring constant (stiffness) | newtons per metre (N/m) |
A stiffer spring has a larger spring constant k, so a greater force is needed to produce the same extension. If you exceed the elastic limit, the spring becomes permanently deformed and no longer obeys Hooke’s law.
较硬的弹簧具有较大的弹性系数 k，因此要产生同样的伸长量就需要施加更大的力。如果超过了弹性极限，弹簧就会发生永久形变，不再遵循胡克定律。
6. Forces and Resultant Force | 力与合力
A force is a push or pull that can change an object’s speed, direction or shape. When several forces act on a body, we can replace them with a single resultant force that has the same effect. Forces are vector quantities, so direction is important.
力是一种推或拉，可以改变物体的速度、方向或形状。当多个力同时作用在一个物体上时，我们可以用一个具有相同效果的合力来代替它们。力是矢量，因此方向很关键。
resultant force = sum of forces in one direction − sum of forces in opposite direction
If the resultant force is zero, the object is in equilibrium – it remains at rest or moves with constant velocity (Newton’s first law).
如果合力为零，物体就处于平衡状态——它将保持静止或匀速直线运动（牛顿第一定律）。
If the resultant force is not zero, the object accelerates in the direction of the resultant force. The bigger the mass, the smaller the acceleration for the same force (this idea leads to Newton’s second law: F = m × a, which you will explore in later years).
如果合力不为零，物体就会沿合力的方向加速。在合力相同的情况下，质量越大，加速度越小（这一思路引出了牛顿第二定律 F = m × a，你将在高年级深入学习）。
7. Work and Energy Transfer | 功与能量转移
In physics, ‘work’ is done whenever a force moves an object in the direction of the force. Work transfers energy from one store to another. The amount of work done equals the energy transferred.
在物理学中，只要力使物体沿力的方向运动，力就对物体做了“功”。做功意味着能量从一个储能转移到了另一个储能。所做的功等于转移的能量。
work done = force × distance moved in the direction of the force
W = F × d
| Symbol | Quantity | Unit |
|---|---|---|
| W | work done (or energy transferred) | joules (J) |
| F | force | newtons (N) |
| d | distance moved | metres (m) |
Lifting a book onto a shelf does work against gravity and stores gravitational potential energy. Dragging a box across the floor does work against friction, dissipating energy as thermal energy (heat).
将一本书举到书架上，克服重力做了功，并储存了重力势能。在地板上拖动箱子，克服摩擦力做了功，能量以热的形式耗散。
8. Power | 功率
Power measures how fast work is done or how quickly energy is transferred. Two machines can do the same amount of work, but the one that completes the task in a shorter time has a greater power.
功率衡量做功的快慢，或者说能量传递的速率。两台机器可以做同样多的功，但如果其中一台在更短的时间内完成任务，它的功率就更大。
power = work done ÷ time taken
P = W ÷ t
power = energy transferred ÷ time
P = E ÷ t
| Symbol | Quantity | Unit |
|---|---|---|
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