1.7

# Types of work

Besides mechanical work, there are several forms of work in thermodynamic systems.

In Solid : generally γ$≠$σ
- Solids can support a certain shear stress
- In solids, atoms cannot move freely.

When the solid surface is under tension, surface can support some shear stress without increasing the surface noticeably. And the atoms in bulk cannot freely move to surface. This situation is related to surface tension. Creating a new surface is related to surface energy.

Usually in liquids, γ$=$σ
- Liquids cannot support shear stress
- In liquids, atoms move freely to surface and adopt a new     configuration.

For example, when the liquid surface is under tension, the atoms in bulk will move to the surface creating new surface. Therefore, surface tension is the same with the surface energy.