Properties of materials
Density, stiffness, expansion and melting point for the materials the ladder makes, and what each number decides.
Home: Building materials, Level 2 · Forge, level 1 of 2 in its track. Serves 7 steps across 3 subjects.
Four numbers decide most design choices: how heavy a material is, how stiff, how much it grows when heated, and where it melts. The values below are the standard ones from OpenStax University Physics (densities, stiffness and expansion) and PubChem (melting points of the metals). Real materials vary with how they were made: timber with species and moisture, steel with its carbon, concrete with its mix.
The table
Stiffness is Young's modulus: the stress needed to stretch a material by a given fraction. A higher number bends less under the same load.
| Material | Density (kg/m³) | Stiffness (GPa) | Expansion (millionths per °C) | Melts |
|---|---|---|---|---|
| Iron and steel | 7,860 | 200–210 | 12 | 1,538 °C (iron) |
| Copper | 8,920 | 110 | 17 | 1,085 °C |
| Brass | 8,440 | 90 | 19 | — |
| Aluminium | 2,700 | 70 | 25 | 660 °C |
| Lead | 11,300 | 16 | 29 | 327 °C |
| Glass (ordinary) | 2,600 | 60 (crown glass) | 9 | Softens at about 720 °C |
| Granite | 2,700 | 45 | — | — |
| Concrete | 2,400 | 20 | 12 | — |
| Brick | — | 15 | 12 | — |
| Hardwood (oak) | 710 | 15 | — | Burns |
| Softwood (pine) | 373 | — | — | Burns |
| Water | 1,000 | — | — | 0 °C, boils at 100 °C |
What the numbers decide
- Steel and concrete expand by the same amount, 12 millionths per °C. That is why steel bars can be cast inside concrete: heat and cold do not tear them apart. See cement and concrete.
- Steel is ten times stiffer than oak but more than ten times heavier, which is why timber frames are still built: see framed buildings.
- Lead melts at 327 °C and copper at 1,085 °C, which set the order in which metals were first worked: see smelting.
- Ordinary glass expands 9 millionths per °C and cracks under sudden heat; borosilicate glass, at 3, survives it.
- A 10 m steel rail grows 1.2 mm for every 10 °C, which is why rails and bridges need expansion gaps.
Where to go next
This page covers what you are most likely to meet. It is not a field guide, and on identification that difference can kill you. These are the works that go further — chosen because they can be held offline.
Still to come
Illustrations carry a technique further than prose, but some things only move well. Recorded here rather than left implicit.
- Tensile and compressive strengths, with the safety factors used for each material