Most objects, even if they're made out of hard materials such as metal, will exhibit some elastic behavior. This is because the forces between the atoms making up the objects act like tiny springs, stretching and compressing in response to an applied force. There are other ways objects can be deformed in addition to simply changing in length.
Objects can also change in volume, if they experience a force from all sides.
Stress and strain The different kinds of deformation can all be related through the idea of stress and strain. When the strain is directly proportional to the applied stress, the object behaves elastically, and will return to its original shape when the stress is removed. For elastic deformation, then, there is a linear relationship between the stress and strain. The pressure unit is known as the pascal. Hooke's law Hooke's law states that strain is proportional to stress, so it applies to elastic deformation, and to the equations concerning stretching, shear, and volume deformation.