Final answer:
Deformation is the change in shape when stress is applied to a rock, and strain is another term for this change. There are three main types of stress: compressional, tensional, and shear. Stress leads to deformation which may be elastic (temporary) or plastic (permanent).
Step-by-step explanation:
When a stress is applied to a body of rock, it commonly changes its shape. A change in shape is a deformation. Another term used to describe a change in shape is strain. Stress and strain are concepts from physics that describe the forces on objects undergoing deformation and the deformation itself, respectively. Stress is the force per unit area applied to a material, and strain is the change in shape that results from this force.
There are three main types of stress: compressional, tensional, and shear. Compressional stress pushes rocks together, tensional stress pulls rocks apart, and shear stress involves rocks moving horizontally past each other in opposite directions. The type of stress determines the resulting deformation, whether the rock exhibits elastic behavior (returning to its original shape) or plastic deformation (permanent change in shape).
Moreover, thermal stress created by thermal expansion or contraction can lead to deformation, and is relevant in the study of metamorphic rocks which form under new pressure and temperature conditions, exemplifying a change in form.