Have you ever come across a situation where you had to struggle to open any jar, but because of its tight lid, you failed to open it? You tried with the tight grip or asked someone else with stronger hands to open it and but still, you were not successful. Eventually, you had to recall the old method and put some hot water on the lid and finally, it opened easily. But, how did it work? The reason behind it is the thermal expansion.
Thermal expansion is a phenomenon in which the change in volume, area, and shape of any matter occurs when the change in its temperature takes place. Temperature is an average molecular kinetic energy of a substance. When any substance is heated, the kinetic energy of its molecule increases simultaneously; this makes the molecules to move faster on an average. The molecules take more space and tend to move in the area that was empty earlier. Therefore, the size of the object increases.
This is the reason when you heat up the jar, the lid expands. However, both glass and metal expand, but metal expands more than the glass. Therefore, some gap is generated between the threads of jar and lid allowing it to open easily. The coefficient of thermal expansion is the property that determines the extent to which a substance is expanded when it is heated.
The different materials expand in a different amount. For small temperature ranges, the thermal expansion of linear uniform objects is directly proportional to the temperature change. Thermal expansion has got its application in the bimetallic strips that are used for the construction of the thermometers, but when a structural part is heated with length kept constant, it can produce detrimental internal stress.
In another way, the coefficient of thermal expansion can be defined as the fractional change in length per unit increase in temperature. The actual coefficient of the thermal expansion is found through the slope of the tangent of temperature vs length.
The equations of thermal expansion coefficient-