📚 Year 7 SQA Physics: Formulas and Principles Quick Reference | Year 7 SQA 物理：公式定理速查手册
This quick reference handbook is designed for Year 7 (S1) students following the SQA physics curriculum. It brings together the most important formulas and principles you will encounter, from motion and forces to energy, waves and electricity. Keep it handy while you revise, complete homework or prepare for tests – every key relationship is explained with straightforward language and clear examples.
这本速查手册专为学习 SQA 物理课程的 Year 7（S1）学生整理。书中汇集了从运动与力到能量、波和电学中最核心的公式与定理。在你复习、完成作业或准备测验时，随时查阅——每一个关键公式都用简明语言和清晰的例子加以说明。
1. Speed and Velocity | 速度与速率
Average speed is defined as the distance travelled divided by the time taken. If an object moves in a straight line with no change in direction, the magnitude of its velocity equals its speed.
平均速度定义为通过的路程除以所用时间。如果物体沿直线运动且方向不变，其速度的大小就等于它的速率。
v = d / t
Here v stands for speed (or magnitude of velocity), measured in metres per second (m/s); d is the distance in metres (m); and t is the time in seconds (s). The same equation can be rearranged: d = v × t and t = d / v.
这里 v 表示速率（或速度的大小），单位是米每秒 (m/s)；d 是距离，单位是米 (m)；t 是时间，单位是秒 (s)。这个公式可以变形：d = v × t 和 t = d / v。
In everyday situations, speed may be given in kilometres per hour (km/h). To convert km/h to m/s, divide by 3.6. For example, a car moving at 72 km/h has a speed of 72 ÷ 3.6 = 20 m/s.
在日常生活中，车速常以千米每小时 (km/h) 表示。将 km/h 换算为 m/s 只需除以 3.6。例如，一辆以 72 km/h 行驶的汽车，其速率为 72 ÷ 3.6 = 20 m/s。
2. Acceleration | 加速度
Acceleration tells us how quickly the velocity of an object changes. It is a vector quantity, meaning it has both magnitude and direction. For motion in a straight line, uniform acceleration can be calculated with the formula:
加速度描述物体速度变化的快慢。加速度是矢量，既有大小也有方向。在直线运动中，匀加速度可用以下公式计算：
a = (v − u) / t
Where a is acceleration in metres per second squared (m/s²), v is final velocity (m/s), u is initial velocity (m/s), and t is the time taken for the change in seconds (s). A positive value means speeding up, while a negative value indicates slowing down (deceleration).
其中 a 为加速度，单位是米每二次方秒 (m/s²)；v 为末速度 (m/s)；u 为初速度 (m/s)；t 为速度变化所用的时间 (s)。正值表示加速，负值表示减速。
If a cyclist accelerates from rest (u = 0) to 10 m/s in 5 s, the acceleration is a = (10 − 0) / 5 = 2 m/s². This means the velocity increases by 2 m/s every second.
如果一名骑行者从静止 (u = 0) 开始，在 5 s 内加速到 10 m/s，则加速度为 a = (10 − 0) / 5 = 2 m/s²。这意味着速度每秒增加 2 m/s。
3. Newton’s Second Law | 牛顿第二定律
Newton’s Second Law describes how an object accelerates when an unbalanced force acts on it. The law is often written as:
牛顿第二定律描述了物体在受到非平衡力作用时如何加速。这一定律常写作：
F = m × a
In this relationship, F is the resultant force in newtons (N), m is the mass in kilograms (kg), and a is the acceleration in metres per second squared (m/s²). A force of 1 N will give a mass of 1 kg an acceleration of 1 m/s².
在这个关系中，F 为合力，单位是牛顿 (N)；m 为质量，单位是千克 (kg)；a 为加速度，单位是 m/s²。1 N 的力能使 1 kg 的物体产生 1 m/s² 的加速度。
To find the force needed to accelerate a 1200 kg car at 2.5 m/s², we multiply: F = 1200 × 2.5 = 3000 N. The forces acting on the car must be combined first to identify the unbalanced force.
要使一辆 1200 kg 的汽车产生 2.5 m/s² 的加速度，所需力为：F = 1200 × 2.5 = 3000 N。必须先合算所有作用在汽车上的力，以确定非平衡力。
4. Weight and Gravitational Field Strength | 重量与引力场强
Weight is the force of gravity pulling on a mass. It should not be confused with mass, which is the amount of matter in an object. Weight can be calculated using:
重量是引力作用于物体上的力，不可与质量混淆，质量是物体所含物质的多少。重量可用下式计算：
W = m × g
Here W is weight in newtons (N), m is mass in kilograms (kg), and g is the gravitational field strength. On Earth’s surface, g is approximately 9.8 N/kg, but for many S1 calculations we use 10 N/kg to keep numbers simple.
这里 W 为重量 (N)，m 为质量 (kg)，g 为引力场强。在地球表面，g 约为 9.8 N/kg，但在 S1 阶段的许多计算中，为简化常取 10 N/kg。
The Moon’s gravitational field strength is about 1.6 N/kg, so an astronaut with a mass of 70 kg would weigh W = 70 × 1.6 = 112 N on the Moon, compared to about 700 N on Earth. Mass remains the same everywhere.
月球的引力场强约为 1.6 N/kg，因此一名 70 kg 的宇航员在月球上重 W = 70 × 1.6 = 112 N，而在地球上则重约 700 N。质量在任何地方都保持不变。
5. Density | 密度
Density measures how much mass is packed into a given volume. Substances with tightly packed particles have higher densities. The formula is:
密度衡量单位体积内所含物质的质量。粒子排列紧密的物质密度较大。公式为：
ρ = m / V
The symbol ρ (Greek letter rho) represents density in kilograms per cubic metre (kg/m³), but you might also use grams per cubic centimetre (g/cm³). m is mass (kg or g), and V is volume (m³ or cm³).
符号 ρ（希腊字母 rho）代表密度，单位是千克每立方米 (kg/m³)，但也可用克每立方厘米 (g/cm³)。m 为质量 (kg 或 g)，V 为体积 (m³ 或 cm³)。
To convert between common units: 1 g/cm³ = 1000 kg/m³. Water has a density of about 1.0 g/cm³ (1000 kg/m³). An object with a density less than water will float; one with a density greater will sink.
常用单位的换算关系为：1 g/cm³ = 1000 kg/m³。水的密度约为 1.0 g/cm³ (1000 kg/m³)。密度小于水的物体会漂浮，大于水的则下沉。
6. Pressure | 压强
Pressure tells us how concentrated a force is over a surface. A small area gives a large pressure for the same force. The pressure formula is:
压强表示作用在表面上的力集中程度。同样的力作用在较小的面积上会产生较大的压强。压强公式为：
p = F / A
p is pressure in pascals (Pa), where 1 Pa = 1 N/m²; F is the force in newtons (N), and A is the area over which the force is spread in square metres (m²).
p 为压强，单位是帕斯卡 (Pa)，1 Pa = 1 N/m²；F 为力 (N)；A 为受力面积 (m²)。
When the same force is applied, a sharp knife (small area) cuts better than a blunt one because the pressure is higher. Studs on football boots increase pressure on the ground to improve grip.
当施加相同的力时，锋利的小刀（面积小）比钝刀切割效果更好，因为压强更大。足球鞋的鞋钉增大了对地面的压强，从而增强抓地力。
7. Kinetic Energy and Gravitational Potential Energy | 动能与重力势能
Energy is the ability to do work. Two important mechanical forms are kinetic energy (energy of motion) and gravitational potential energy (energy stored due to height).
能量是做功的本领。两种重要的机械能形式是动能（运动具有的能量）和重力势能（因高度而储存的能量）。
Kinetic Energy: Eₖ = ½ × m × v²
Eₖ is kinetic energy in joules (J), m is mass in kilograms (kg), and v is speed in metres per second (m/s). Notice that doubling the speed increases kinetic energy by a factor of four.
Eₖ 为动能，单位焦耳 (J)；m 为质量 (kg)；v 为速率 (m/s)。注意，速度加倍会使动能变为原来的四倍。
Gravitational Potential Energy: Eₚ = m × g × h
Eₚ is potential energy in joules (J), m is mass (kg), g is gravitational field strength (N/kg) and h is the height above a reference point in metres (m).
Eₚ 为重力势能 (J)；m 为质量 (kg)；g 为引力场强 (N/kg)；h 为相对参考点的高度 (m)。
When a ball is dropped, the gravitational potential energy is converted into kinetic energy. Ignoring air resistance, the total mechanical energy stays constant – this is the principle of conservation of energy.
当球下落时，重力势能转化为动能。不计空气阻力，总机械能保持不变——这就是能量守恒定律。
8. Work and Power | 功与功率
Work is done when a force moves an object through a distance in the direction of the force. The amount of work transferred is calculated by:
当力使物体沿力的方向移动一段距离时，力做了功。传递的功的大小由下式计算：
W = F × d
W is work in joules (J), F is the force applied in newtons (N), and d is the distance moved in metres (m). Note that if the force and motion are perpendicular, no work is done.
W 为功 (J)；F 为施加的力 (N)；d 为物体在力的方向上移动的距离 (m)。注意，如果力与运动方向垂直，则不做功。
Power is the rate at which work is done or energy is transferred. The formula is:
功率是做功或能量转化的快慢。公式为：
P = W / t
P is power in watts (W), where 1 W = 1 J/s, W is work done (or energy transferred) in joules (J), and t is time in seconds (s). A powerful machine does the same work in less time.
P 为功率，单位瓦特 (W)，1 W = 1 J/s；W 为做功或转化的能量 (J)；t 为时间 (s)。功率大的机器能在更短的时间内完成相同的功。
9. Wave Speed, Frequency and Wavelength | 波速、频率与波长
All waves transfer energy without transferring matter. The relationship between wave speed, frequency and wavelength is very important:
所有的波传递能量但不传递物质。波速、频率和波长之间的关系非常重要：
v = f × λ
v is the wave speed in metres per second (m/s), f is the frequency in hertz (Hz) – the number of complete waves passing a point per second – and λ (lambda) is the wavelength in metres (m).
v 为波速 (m/s)；f 为频率，单位赫兹 (Hz)，即每秒通过某点的完整波的数量；λ (lambda) 为波长 (m)。
Sound travels at about 340 m/s in air. If a tuning fork produces a sound of 680 Hz, the wavelength can be found: λ = v / f = 340 ÷ 680 = 0.5 m. The equation also works for water waves and light.
声音在空气中传播速度约为 340 m/s。若一支音叉发出 680 Hz 的声音，波长为 λ = v / f = 340 ÷ 680 = 0.5 m。此方程同样适用于水波和光。
Period (T) is the time for one complete wave to pass a point. It is the reciprocal of frequency: T = 1 / f. A wave with a frequency of 50 Hz has a period of 0.02 s.
周期 (T) 是完成一个完整波通过某点所需的时间，是频率的倒数：T = 1 / f。频率为 50 Hz 的波，周期为 0.02 s。
10. Ohm’s Law and Electrical Power | 欧姆定律与电功率
Electric circuits allow current to flow, transferring energy to components. Ohm’s Law relates the voltage across a resistor to the current flowing through it:
电路使电流流动，将能量传递给电路元件。欧姆定律描述了电阻两端的电压与流过电流的关系：
V = I × R
V is potential difference (voltage) in volts (V), I is current in amperes (A), and R is resistance in ohms (Ω). For a fixed resistor, if the voltage doubles, the current also doubles, provided the temperature stays constant.
V 为电压 (V)；I 为电流 (A)；R 为电阻，单位欧姆 (Ω)。对于定值电阻，若温度不变，电压翻倍时电流也翻倍。
Many circuits also use the electrical power formula to describe how quickly a component converts electrical energy into other forms:
许多电路也用到电功率公式，以描述电器将电能转化为其他形式能量的快慢：
P = I × V
P is electrical power in watts (W), I is current (A) and V is voltage (V). Using Ohm’s Law, you can also write: P = I² × R and P = V² / R.
P 为电功率 (W)；I 为电流 (A)；V 为电压 (V)。借助欧姆定律，还可推导出：P = I² × RPublished by TutorHao | Year 7 Physics Revision Series | aleveler.com
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