📚 Physical Properties | 物理性质
Physical properties describe the characteristics of a material that can be observed or measured without changing its chemical identity. They are fundamental to physics and engineering, guiding the selection of materials for construction, electronics, and everyday products. This article explores key physical properties such as density, elasticity, plasticity, hardness, thermal conductivity, and electrical behaviour.
物理性质描述的是在不改变物质化学身份的前提下可以观察或测量的特性。它们是物理学和工程学的基础，指导着建筑材料、电子器件和日常用品的选材。本文将探讨关键物理性质，如密度、弹性、塑性、硬度、导热性和导电行为。
1. Understanding Physical Properties | 理解物理性质
Physical properties are attributes that can be determined without altering the chemical composition of a substance. Common examples include density, colour, melting point, boiling point, electrical conductivity, and hardness. These properties allow scientists and engineers to predict how a material will behave under different conditions.
物理性质是无需改变物质化学成分即可确定的属性。常见例子包括密度、颜色、熔点、沸点、电导率和硬度。这些性质使科学家和工程师能够预测材料在不同条件下的行为。
Physical properties are normally classified into mechanical (strength, elasticity, plasticity), thermal (conductivity, expansion, specific heat), electrical (conductivity, resistivity), and optical (refractive index, transparency) categories. Each category helps in matching a material to its intended use.
物理性质通常分为力学性质（强度、弹性、塑性）、热学性质（导热性、热膨胀、比热容）、电学性质（电导率、电阻率）和光学性质（折射率、透明度）。每一类都有助于使材料与其预期用途相匹配。
2. Density and Its Measurement | 密度及其测量
Density (ρ) is defined as mass per unit volume. It is a scalar quantity that indicates how tightly matter is packed in a substance.
密度（ρ）定义为单位体积的质量，是一个标量，表示物质中物质聚集的紧密程度。
ρ = m / V
where 1 g/cm³ = 1000 kg/m³. The density of water at 4 °C is approximately 1.00 g/cm³.
密度的国际单位是千克每立方米（kg/m³）。另一个常用单位是克每立方厘米（g/cm³），其中1 g/cm³ = 1000 kg/m³。水在4 °C时的密度约为1.00 g/cm³。
For regular objects, volume can be measured by geometric calculation, and mass by a balance. For irregular objects, the water displacement method provides an accurate volume, enabling density determination. Density helps identify substances and assess purity.
对于规则物体，体积可以通过几何计算测量，质量用天平测量。对于不规则物体，排水法可以提供精确的体积，从而测定密度。密度有助于鉴定物质和评估纯度。
3. Elastic Deformation and Hooke's Law | 弹性形变与胡克定律
Elastic deformation occurs when a material returns to its original shape after the applied force is removed. This reversible behaviour is observed in materials like steel and rubber within certain limits.
弹性形变是指施加的力撤除后材料恢复原状的现象。这种可逆行为在一定限度内出现在钢和橡胶等材料中。
Hooke's Law describes the relationship between the applied force and the extension for many elastic materials. The law states that the extension ΔL is directly proportional to the applied force F, provided the proportional limit is not exceeded.
胡克定律描述了许多弹性材料中外力与伸长量之间的关系。该定律指出，只要不超过比例极限，伸长量 ΔL 与所施加的力 F 成正比。
F = k ΔL
Here k is the spring constant, which depends on the material and its dimensions. When the force is plotted against extension, the initial straight line through the origin confirms Hookean behaviour.
式中 k 是弹簧常数，取决于材料及其尺寸。当绘制力与伸长量的关系图时，过原点的初始直线证明了胡克行为。
4. Stress, Strain, and Young's Modulus | 应力、应变与杨氏模量
ain (ε) is the extension per unit original length, ε = ΔL / L&sub0;.
应力（σ）是单位横截面积上的内部恢复力，定义为 σ = F / A。应变（ε）是单位原始长度的伸长量，ε = ΔL / L&sub0;。
Young's modulus (E) quantifies a material's stiffness and is the ratio of tensile stress to tensile strain within the elastic limit:
杨氏模量（E）量化了材料的刚度，是在弹性极限内拉伸应力与拉伸应变之比：
E = σ / ε = (F/A) / (ΔL/L&sub0;)
The unit of Young's modulus is the pascal (Pa). Steel, for instance, has a Young's modulus of about 200 GPa, indicating high stiffness, whereas rubber has a much lower modulus, reflecting its easy stretchability.
杨氏模量的单位是帕斯卡（Pa）。例如，钢的杨氏模量约为200 GPa，表明其刚度很高，而橡胶的模量低得多，反映出它容易拉伸。
5. Plastic Deformation and Yield Point | 塑性形变与屈服点
When the stress exceeds the elastic limit, the material undergoes plastic deformation. In this region, the deformation is permanent; the material does not return to its original shape after the load is removed.
当应力超过弹性极限时，材料发生塑性形变。在此区域，形变是永久性的；卸除载荷后材料不会恢复原始形状。
The yield point (or yield strength) marks the transition from elastic to plastic behaviour. On a stress–strain curve, a distinct yielding region often appears where strain increases rapidly for a small increase in stress.
屈服点（或屈服强度）标志着从弹性行为到塑性行为的转变。在应力-应变曲线上，通常会出现一个明显的屈服区，此时应力小幅增加就会导致应变急剧增大。
Beyond the yield point, materials like mild steel display a plastic plateau and then work hardening before eventual fracture. Understanding yield strength is critical in structural design to prevent permanent deformation.
超过屈服点后，低碳钢等材料会表现出塑性平台，随后加工硬化，最后断裂。理解屈服强度对于结构设计中防止永久变形至关重要。
6. Ductility, Malleability and Brittleness | 延展性、可锻性与脆性
Ductility refers to a material's ability to be drawn into thin wires under tensile stress. Copper and aluminum are highly ductile metals widely used in electrical wiring.
延展性是指材料在拉伸应力下被拉成细丝的能性。铜和铝是高延展性金属，广泛用于电线。
Malleability is the ability of a material to be hammered or rolled into thin sheets without fracturing. Gold is one of the most malleable metals and can be beaten into extremely thin foils.
可锻性是指材料被锤打或轧制成薄片而不断裂的能力。金是最具可锻性的金属之一，能被锤打成极薄的箔片。
Brittleness is the opposite characteristic; brittle materials fracture with little or no plastic deformation. Glass, ceramics, and some cast irons are typical brittle materials that fail suddenly under stress.
脆性是相反的特性；脆性材料在很少或没有塑性变形的情况下断裂。玻璃、陶瓷和某些铸铁是典型的脆性材料，在应力下会突然破坏。
7. Hardness and Its Measurement | 硬度及其测量
Hardness is a measure of a material's resistance to indentation, scratching, or abrasion. It correlates with wear resistance and is an important property in tool design and surface engineering.
硬度是衡量材料抵抗压痕、划痕或磨损的能力。它与耐磨性相关，是工具设计和表面工程中的重要性质。
Several scales are used to quantify hardness. The Mohs scale ranks minerals from 1 (talc) to 10 (diamond) based on scratch resistance. Indentation tests such as Brinell, Vickers, and Rockwell use an indenter under a specified load and measure the indentation size.
有多种标度用于量化硬度。莫氏硬度标根据耐刮擦性将矿物从1（滑石）到10（金刚石）分级。布氏、维氏和洛氏等压痕硬度测试使用特定载荷下的压头并测量压痕尺寸。
Hardness does not always correlate directly with strength; for instance, hardened steel is both strong and hard, but some tough materials may have moderate hardness. Selection depends on the application requirements.
硬度并不总是与强度直接相关；例如，淬火钢既坚固又硬，但某些韧性材料可能具有中等硬度。选择取决于应用要求。
8. Thermal Conductivity and Heat Capacity | 导热性与热容
Thermal conductivity (κ) measures a material's ability to conduct heat. Metals such as copper and silver are excellent thermal conductors, which is why they are used in cookware and heat exchangers. Insulators like wood and foam have low thermal conductivity.
导热性（κ）衡量材料传导热量的能力。铜和银等金属是优良的导热体，因此用于炊具和热交换器。木材和泡沫塑料等绝缘体具有低导热性。
Specific heat capacity (c) is the amount of heat energy required to raise the temperature of 1 kg of a substance by 1 °C (or 1 K). The relationship is:
比热容（c）是使1千克物质温度升高1 °C（或1 K）所需的热量。关系式为：
Q = m c Δθ
Water has a particularly high specific heat capacity (about 4200 J/kg·K), which makes it effective for thermal storage and climate regulation. Materials with low heat capacity heat up quickly.
水的比热容特别高（约4200 J/kg·K），这使其有效用于蓄热和气候调节。低热容的材料升温快。
9. Electrical Conductivity and Resistivity | 电导率与电阻率
tivity (ρ): σ = 1/ρ. High conductivity means low resistance to current flow.
电导率（σ）表示电荷通过材料的容易程度。它是电阻率（ρ）的倒数：σ = 1/ρ。高电导率意味着对电流的阻力低。
Silver is the best metallic conductor, followed by copper and gold. Most metals have resistivities on the order of 10−8 Ω·m, while insulators like rubber have resistivities above 1010 Ω·m. Semiconductors fall in between.
银是最好的金属导体，其次是铜和金。大多数金属的电阻率在10−8 Ω·m量级，而橡胶等绝缘体的电阻率高于1010 Ω·m。半导体介于两者之间。
Superconductivity is a phenomenon where certain materials lose all electrical resistance below a critical temperature. This property has transformative applications in magnets, power transmission, and quantum computing.
超导是一种现象，某些材料在低于临界温度时电阻完全消失。这一性质在磁体、电力传输和量子计算中具有革命性应用。
10. Thermal Expansion | 热膨胀
Most materials expand when heated and contract when cooled. The linear expansion of a solid can be described by the equation:
大多数材料受热膨胀、遇冷收缩。固体的线性膨胀可用以下方程描述：
ΔL = α L&sub0; Δθ
where ΔL is the change in length, L&sub0; the original length, Δθ the temperature change, and α the coefficient of linear expansion characteristic of the material.
式中 ΔL 是长度变化，L&sub0; 是原始长度，Δθ 是温度变化，α 是材料特有的线膨胀系数。
Concrete and steel have similar expansion coefficients, allowing them to be used together in reinforced concrete. Expansion joints in bridges and railway tracks accommodate thermal movement and prevent structural damage.
混凝土和钢材具有相近的膨胀系数，使它们能一起用于钢筋混凝土。桥梁和铁轨的伸缩缝可适应热运动，防止结构损坏。
11. Summary of Key Physical Properties | 主要物理性质小结
A material's physical properties determine its suitability for specific applications. Engineers must consider density for lightweight design, elastic modulus for stiffness, yield strength for safety, and thermal and electrical conductivities for energy systems.
材料的物理性质决定了它是否适合特定应用。工程师必须考虑轻量化设计中的密度、刚度对应的弹性模量、安全性对应的屈服强度以及能源系统中的导热性和电导率。
By understanding the relationships among stress, strain, hardness, brittle and ductile behaviour, and response to temperature, scientists and engineers can tailor materials for everything from microelectronics to skyscrapers. Mastery of physical properties is therefore essential in both academic physics and practical engineering.
通过理解应力、应变、硬度、脆性和延性行为以及对温度的响应，科学家和工程师可以为从微电子到摩天大楼的各种需求定制材料。因此，掌握物理性质在学术物理和实际工程中都是必不可少的。
Published by TutorHao | Physics Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图