📚 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) |
lways 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
ated 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）。
igger 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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