| Component (of a vector): | (english) Any vector can be expressed as a collection of vectors whose sum is equal to the original vector. Each vector in this collection is a component of the original vector. It is common to express a vector in terms of components which are parallel to the x and y axes. |
| Concentrated force: | (english) A force considered to act along a single line in space. Concentrated forces are useful mathematical idealizations, but cannot be found in the real world, where all forces are either body forces acting over a volume or surface forces acting over an area. |
| Couple: | (english) A system of forces composed of two equal forces of opposite direction, offset by a distance. A couple is statically equivalent to a moment whose magnitude equals the magnitude of the force times the offset distance. |
| Deflection: | (english) This word usually carries the same meaning as displacement, although it is sometimes used in place of deformation. |
| Degree of Freedom: | (english) A displacement quantity which defines the shape and location of an object. In the two dimensional plane, a rigid object has three degrees of freedom: two translations and one rotation. In three dimensional space, a rigid object has six degrees of freedom (three translations and three rotations). |
| Displacement: | (english) A change in position. A displacement may be a translation a rotation or a combination of those. |
| Distributed load: | (english) An external force which acts over a region of length, surface, or area: essentially any external force which is not a concentrated force. |
| Ductility: | (english) Ductility generally refers to the amount of inelastic deformation which a material or structure experiences before complete failure. Quantitatively, ductility can be defined as the ratio of the total displacement or strain at failure, divided by the displacement or strain at the elastic limit. |
| Dynamic equilibrium: | (english) Equilibrium which includes inertial forces. |
| Elastic: | (english) A material or structure is said to behave elastically if it returns to its original geometry upon unloading. |