At the microscopic scale, a solid has these properties:
- The atoms  or molecules  that comprise the solid are packed close together.
- These constituent elements have fixed positions  in space relative to each other. This accounts for the solid's rigidity.
- If sufficient force is applied, either of these properties can be violated, causing permanent deformation.
- Because any solid has some thermal energy, its atoms vibrate. However, this movement is very small and very rapid, and cannot be observed under ordinary conditions.
The branch of physics  that deals with solids is called solid-state physics , and is a type of condensed matter physics . Materials science  is primarily concerned with properties of solids such as strength and phase  transformations. It overlaps strongly with solid state physics. Solid-state chemistry  overlaps both of these fields, but is especially concerned with the synthesis of novel materials.
The lightest known solid is man-made and is called aerogel. The lightest aerogel produced has a density of 1.9 mg per cm3 or 1.9 kg/m3 (526.3 times lighter than water).
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