Thermal expansion
Heat → particles vibrate more → spacing increases → solid expands. Gas expands the most.
Why? Heating gives particles more KE, so they vibrate further from each other on average → material expands.
Order of expansion: gases (most) > liquids > solids (least). Gases have weak forces and free particles, so expansion is dramatic.
Practical consequences.
- Bridges: have expansion gaps to allow concrete to expand on hot days without buckling.
- Bimetallic strip: two metals with different expansion rates bonded together. On heating, the strip BENDS (towards the slower-expanding metal). Used in thermostats.
- Thermometers (liquid-in-glass): mercury or coloured alcohol expands up a thin tube. Read off the temperature from the column height.
Worked qualitative. Why do tightly closed glass bottles sometimes crack on heating? Liquid expands more than glass. The trapped liquid pushes outward → glass cracks.
- Gas > liquid > solid in expansion.
- Bimetallic strip bends — used in thermostats.
- Bridges have expansion gaps.
- Liquid-in-glass thermometers exploit liquid expansion.