Physics – 2.2.1 Thermal expansion of solids, liquids and gases | e-Consult

Thermal expansion is the tendency of matter to change in volume in response to a change in temperature. Many everyday applications rely on this principle.

Examples include:

• Bimetallic Strips: These are made of two different metals bonded together, with different coefficients of thermal expansion. When heated, the metal with the higher coefficient expands more, causing the strip to bend. This bending is used in thermostats (to control temperature in heaters and refrigerators), circuit breakers (to interrupt the flow of electricity if the current is too high), and oven timers. The difference in expansion causes the strip to move, triggering the desired action.
• Expansion Joints in Bridges and Roads: Bridges and roads are built with expansion joints – gaps that allow for thermal expansion and contraction. Without these joints, the stress caused by expansion and contraction could lead to cracking and structural failure. The joints accommodate the change in length without putting excessive strain on the structure.
• Expansion in Railways: Similar to bridges, railway tracks have small gaps (expansion gaps) between sections of rail. These gaps allow the rails to expand in hot weather without buckling. This prevents derailments and maintains the track's integrity.
• Loosening of Jar Lids: Warming a glass jar lid with warm water causes the metal lid to expand slightly. This reduces the friction between the lid and the glass, making it easier to open.

The applications work because the materials are designed to exploit the predictable expansion and contraction associated with temperature changes. The differing coefficients of expansion, or the inclusion of gaps, allows for the controlled movement and stress relief needed in these applications.