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Thermal Expansion
Thermal expansion is caused by heating solids, liquids or gases, which makes the particles move faster or vibrate more (for solids). This means that the particles take up more space and so the substance expands.
Some everyday effects of thermal expansion are useful, but some are just a plain nuisance. Here are five examples:
1) If you have ever tried to unscrew a stuck lid off a glass jar, you'll appreciate this expansion effect. Simply run some hot water over the metal lid for a few seconds to heat the lid up. This will make the lid expand slightly and it should then be easier to unscrew.
2) Bridges have a long span and in hot weather the materials that the bridge is made of will expand. This could cause the bridge span 'sections' to buckle.
To avoid this, expansion joints are designed into the bridge so that the bridge sections can expand freely without buckling.
3) A liquid, when heated, will expand and can be made to rise up a tube. Thermometers use the expansion of a liquid such as mercury or alcohol to measure the temperature using a calibrated scale.
4) The cables that hang between electricity pylons must have some slack on them. This to avoid the cables becoming too tight and breaking in cold weather when the cable material contracts.
You can sometimes see these cables sag in hot weather.
5) A bimetallic strip has two metal strips glued together. One of these metals expands more for each degree temperature rise than that other. This causes the bimetallic strip to curve as it is heated.
This movement can act as an electrical switch by connecting a circuit, for example to turn on a fan, if the room temperature gets too hot.
Other examples of thermal expansion include:
- The air in a car tyre gets warm after a long journey and this increases its pressure.
- Railway lines require expansion gaps (similar to bridges) to avoid buckling in hot weather.
GCSE Physics Keywords: Thermal expansion, heat