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CSEC Physics: Thermal Expansion

In this lesson, we will cover:

  • explaining why the effects of thermal expansion occur

  • applications of thermal expansion

Thermal expansion is a fractional change in size (volume) of a material in response to a change in temperature. For most materials, over small temperature ranges, these fractional changes:

  • are directly proportional to change in temperature (∆T)

  • have the same observed change (i.e., materials usually expand when heated and contract when cooled)

  • are larger for liquids than solids

When a material is heated, it increases the kinetic energy of the particles, causing them to move around and vibrate more. So, the particles take up more space and the substance/material expands.

Thermal expansion can be very useful, however, it can also be an obstacle for which designers and architects must take into consideration. Here are some examples of thermal expansion's applications in day to day life:

  1. When opening the lid of a jar when its stuck, if you run hot water over it to heat it up, it will make it easier to open. This is because the lid expands slightly when heated due to thermal expansion, making it easier to unscrew.

  2. Bridges span long distances, and in hot weather, the materials will expand. This would cause the bridge to buckle. However, architects compensate for this by adding expansion joints that can expand freely without buckling.

  3. A liquid, when heated, will expand. This liquid, when placed in a tube, will rise up the tube. Thermometers will use liquids such as mercury or alcohol and their thermal expansions to measure temperature on a calibrated scale.

  4. The cables that hang between electricity poles (pylons) must have some slack on them. This is so that in cold weather (when the cables contract) they don't become too tightly-drawn and break. You will also notice that in hot weather, the cables will sag due to thermal expansion.

  5. Roofs are usually made up of individual slates that may make creaking noises throughout the day. As temperatures change, such as cooling at night or heating during the day, thermal expansion or contraction of the slates may cause movement that in turn causes snapping, popping, or cracking noises, even bangs and clanks or clicks from the roof.

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