When explaining thermal expansion of a substance it is helpful to understand that, at least to my knowledge, there are two types of thermal expansion: Linear and Volumetric. Linear expansion is what happens when you have a solid rod of any one substance, for example: rebar, and how much it elongates or shortens depending on the amount of heat absorbed or released. Volumetric expansion is what happens when you have any sort of substance in any shape or size and how much it expands or contracts depending on the amount of heat absorbed or released.
Linear expansion is best used under situations dealing with, as stated above, rod shaped substances. This is best used in applications where the substance is a metallic in nature. Generally, this method is used for solids that are formed into rod shapes.
When talking about linear expansion it is good to understand the equations behind the explanation because they give an extra dimension of depth for understanding. The change in length of any substance with a rod shaped form (L), is expressed by the change in temperature (T) multiplied by the initial length (L) multiplied by the coefficient of linear expansion (*). The formula is expressed as:
L= Lx*xT
Volumetric expansion is best used under all situations other than those under which linear expansion applies and is best. The best use of this would be in applications for any substance. Generally, however, this method is usually used for liquids and gasses, as the linear method would fail because liquids and gasses do not hold their own shape but form into the space around them.
As it was good to know the formula for linear expansion, so too are the reasons for knowing the formula for volumetric expansion as well. Volumetric expansion is defined as the change of volume of any substance (V), which is expressed by multiplying the change in temperature (T) by the initial volume (V) multiplied by the coefficient of volumetric expansion (#). The formula for volumetric expansion is as follows:
V= Vx#xT
The point is that the thermal expansion of a substance is directly proportional to the change in temperature of that substance; meaning that when a substance absorbs heat, it expands, when a substance releases it, the substance contracts. Of course there are exceptions to this rule. Water, for example, is the most notable exception because it is a well known fact that, when frozen, water expands which is an inverse to the volumetric expansion principle.
