Properties of Materials: Density, Conductivity and Uses | 材料的性质：密度、导电性与用途

2026-08-21 13:36 · 本文部分内容由AI辅助创作

📚 Properties of Materials: Density, Conductivity and Uses | 材料的性质：密度、导电性与用途

This revision note supports Cambridge Lower Secondary Science Chapter 2, pages 24-41. Materials are the substances from which every object is made. To choose the best material for a job, scientists and engineers examine its properties, such as density, melting point, strength, and conductivity.

本复习笔记对应 Cambridge Lower Secondary Science 第 2 章第 24-41 页。材料是构成所有物体的物质。为了给某个用途选择最佳材料，科学家和工程师会考察材料的性质，例如密度、熔点、强度和导电性。

1. Physical and Chemical Properties | 物理性质与化学性质

A physical property can be observed or measured without changing the substance into a new substance. Examples include colour, density, hardness, melting point, and conductivity. A chemical property describes how a substance reacts with others, such as flammability or reaction with acid.

物理性质是可以观察或测量而不使物质变成新物质的性质。例如颜色、密度、硬度、熔点和导电性。化学性质描述物质与其他物质反应的方式，例如可燃性或与酸反应。

Physical properties: density, melting point, strength, electrical conductivity, thermal conductivity.
Chemical properties: flammability, reaction with water, reaction with acid, rusting.

物理性质：密度、熔点、强度、导电性、导热性。

化学性质：可燃性、与水反应、与酸反应、生锈。

2. Density and the Density Equation | 密度与密度公式

Density measures how much mass is packed into a certain volume. A material is more dense if its particles are closely packed or if its atoms are heavier for the same space.

密度测量一定体积内含有多少质量。如果粒子的排列更紧密，或相同空间内原子更重，材料的密度就更大。

Density = mass ÷ volume

ρ = m ÷ V

Mass is measured in grams (g) or kilograms (kg). Volume is measured in cubic centimetres (cm³) or cubic metres (m³). Density is therefore given in g/cm³ or kg/m³.

质量以克（g）或千克（kg）为单位。体积以立方厘米（cm³）或立方米（m³）为单位。因此密度的单位是 g/cm³ 或 kg/m³。

For example, a 10 cm³ block of aluminium has a mass of 27 g. Its density is calculated as follows:

例如，一块 10 cm³ 的铝块质量为 27 g。其密度计算如下：

ρ = 27 g ÷ 10 cm³ = 2.7 g/cm³

3. Density in Solids, Liquids, and Gases | 固体、液体和气体的密度

In general, solids have higher densities than liquids, and liquids have higher densities than gases. This pattern occurs because solids have particles very close together, while gas particles are far apart and can be compressed.

一般来说，固体的密度大于液体，液体的密度大于气体。这是因为固体中的粒子非常紧密，而气体粒子相距很远并且可以被压缩。

Water is an important exception: ice floats on liquid water because the solid form is less dense. In ice, hydrogen bonds hold water molecules in an open lattice that takes up more space.

水是一个重要的例外：冰浮在液态水上，因为固态水的密度较小。在冰中，氢键使水分子保持在占据更多空间的开放晶格中。

4. Melting and Boiling Points | 熔点与沸点

The melting point is the temperature at which a solid changes to a liquid. The boiling point is the temperature at which a liquid changes to a gas. Pure substances have sharp melting and boiling points, but mixtures often melt or boil over a range of temperatures.

熔点是固体变成液体的温度。沸点是液体变成气体的温度。纯净物具有明确的熔点和沸点，但混合物通常在一个温度范围内熔化或沸腾。

Materials with strong bonds between particles, such as diamond or most metals, have high melting points. Materials made of small molecules, such as wax or oxygen, have weak attractions and lower melting points.

粒子间结合力强的材料（如金刚石或大多数金属）具有高熔点。由小分子组成的材料（如蜡或氧气）分子间作用力弱，因此熔点较低。

5. Thermal Conductivity | 导热性

Thermal conductivity measures how well a material transfers heat. Metals are good thermal conductors because their free electrons can carry energy quickly. Wood, plastic, glass, and air are thermal insulators.

导热性衡量材料传递热量的能力。金属是良好的导热体，因为它们的自由电子可以快速携带能量。木材、塑料、玻璃和空气是热的绝缘体。

This is why saucepans are often made of metal, but their handles are covered with plastic or wood to reduce heat transfer to the hand.

这就是为什么炖锅通常由金属制成，但锅柄覆盖塑料或木材，以减少向手部传热。

Material	Thermal conductivity	Typical use
Copper	Excellent conductor	Pan base, heat exchanger
Wood	Insulator	Handle, spoon
Air	Good insulator	Double glazing, clothing

广告 / Sponsored

DK汽车大百科升级修订版儿童科普百科

¥372.1

📱 去京东购买

京东精选

6. Electrical Conductivity | 导电性

Electrical conductivity describes how easily a material allows an electric current to flow. Metals and graphite are conductors because they contain charged particles that can move. Most non-metals, plastics, rubber, and glass are insulators.

导电性描述材料允许电流通过的难易程度。金属和石墨是导体，因为它们含有可以移动的带电粒子。大多数非金属、塑料、橡胶和玻璃是绝缘体。