Line of Action
The line along which the force acts
Principle of Transmissibility
A force vector can be considered to act with the same external effect on a body, anywhere along the line of action of the force
Moment Center
The point about which a moment is calculated
Moment of a Force
The tendency of a force to cause rotation of a body about a point or axis
Concurrent Force System
A system in which the lines of action of all forces intersect at one point
Non-Concurrent Force System
A system in which the lines of action of all forces do not intersect at one point
Static Equilibrium
A state in which all forces and moments acting on a system are balanced
Load
An externally applied force or couple moment
Support
A physical connection between a body and its surroundings
Reaction
A force or couple moment that is exerted on a body by a support
Frame
A stationary structure, the primary purpose of which is to carry load
Machine
An assembly of moving parts, the primary purpose of which is to transmit and/or magnify forces
Multi-Force Member
A member that is acted upon by forces applied at more than two points, or by both forces and moments
Two-Force Member
A member connected at its ends by frictionless pins and has forces applied only at these ends (and no applied moments)
Mechanical Advantage
The force amplification achieved by using a machine
Truss
A structure composed of straight, slender members joined together at their end points and loaded only at the joints
Stress
The measure of the intensity of an internal force
Normal Stress
Stress which is oriented perpendicular to the section plane
Shear Stress
Stress which is oriented parallel to the section plane
Strain
The measure of the intensity of the deformation
Modulus of Elasticity
A material property representing the slope of a typical stress-strain curve in the elastic region
Hooke's Law
The linear relationship between normal stress and normal strain
Poisson's Ratio
A material property representing the ratio of lateral to longitudinal strain
Deformation
A change in the dimensions or shape of a body