These conventions allow us to express reactions between different elements and compounds very succinctly. These springs can absorb and store energy just like ordinary coil springs with which you are familiar. This describes the property of the material which we call stiffness. Stiffness can be thought of as the property that describes how a material resists deformation or change in shape. The ultimate strength of a material is the force required to break or fracture the material, to separate the particles from which it is made.
Strength is the property of a material that describes how it resists forces.
The three basic types forces are tension, compression and shear. We need to know which type of force is applied to a material because materials differ in their ability to resist them. When a force is applied to a material it may deform before it breaks. Plasticity is the opposite of elasticity. The deformation which accompanies a tensile force is called elongation or lengthening, while that accompanying a compressive force is called shortening.