What is thermal expansion?

Answer 1

Thermal expansion is the physical change of size of something owing to higher thermal energy of the object. Heat (thermal energy) causes increased atomic motion in materials, and this change in the kinetic energy of the atoms and molecules of a material will cause it to increase in volume.

It is a physical characteristic of matter (as opposed to a chemical one), and it is pretty much true across the board. No, ice does not expand when it turns to water, and there are a couple of other exceptions, but, in general, when we heat things, they increase in volume. So the density will decrease but mass remains the same. As in the density formulae, Density= Mass over Volume. When mass do not change and volume increases, it is obvious that it had density to be lower.

Answer 2

Thermal Expansion causes the molecules in a given mass of a certain substance to move further apart (because they are vibrating more, they occupy a larger molecular shadow, and so repel other molecules in a larger area, but with the same force).

Answer 3

Heat is the average kinetic energy of the molecular (or sub-molecular) consituents of matter. The faster the molecules are vibrating, the hotter the material is. And faster vibrations are going to have larger amplitudes as well, so the molecules will take up more space, and the size of the object therefore increases as it gets hotter - in most cases. Phase changes can cause other effects, such as the well-known phenomenon that water increases in volume as it freezes, because ice has a crystaline structure that takes up more room than liquid water. But it is still true that as the ice gets progressively colder, it shrinks, just like any other material substance.

Answer 4

Kinetic Energy will [always] do this.

Answer 5

Heat