Laws of Forces - Structural Systems

Vocabulary flashcards defining fundamental concepts, classifications, elements, and laws of force systems based on the lecture notes.

Force

An abstract action that moves or tends to move, stops or tends to stop the motion of an object, or changes its direction, shape, or size.

Point of Application

The exact location at which a force is applied to a body, usually described by coordinates and represented graphically by the tip of an arrowhead.

Magnitude

The numerical size of a force expressed in units such as pounds (lbs), kips ($1\,\text{kip} = 1000\,\text{lbs}$), newtons ($\text{N}$), or kilo-newtons ($1\,\text{KN} = 1000\,\text{N}$).

Graphic Statics

A method of structural analysis where accurately drawing the magnitude of force vectors to scale is the essential core technique.

Line of Action

A characteristic, indefinitely long line along which a force acts, described using a reference axis for orientation.

Sense

The specification of the direction (positive or negative, such as upward or downward) in which a force moves along its line of action.

Contact Forces

Forces that result from physical contact between two objects where one object exerts force on the other, such as the pressure of steam in a cylinder.

Non Contact Forces

Forces that act without physical contact between objects, such as magnetic, electrical, and gravitational forces.

Applied Force

A force produced by the action of muscles, also referred to as muscular force.

Normal Force

A contact interaction force between surfaces that acts perpendicular to and out of the surface, arising from the microscopic deformation of molecules.

Frictional Force

A contact force resulting from interactions with a surface when an object moves or attempts to move relative to that surface.

Tension Force

An applied pulling force exerted through a string, cable, or rope that cannot push and is assumed to be uniform throughout.

Air Resistance Force

A force acting in opposition to motion through a gas due to cumulative interactions with air molecules, increasing with higher velocity and surface area.

Spring Force

A force arising from molecular displacement that acts in the direction opposite to the displacement of the spring.

Gravitational Force

An attractive non-contact force exerting between two objects that originates with the presence of matter.

Electromagnetic Force

A non-contact force encompassing basic electric and magnetic interactions responsible for binding atoms and the structure of solids.

Force System

A condition or problem in mechanics where more than one force acts on an object or structure.

Coplanar Force System

A force system in which the lines of action of all acting forces lie within a single plane.

Non-Coplanar Force System

A force system in which the lines of action of the forces do not all lie in the same plane.

Collinear Force System

A force system in which the lines of action of all forces act along the exact same straight line.

Concurrent Force System

A force system where the lines of action of all forces, when extended, pass through a single common point called the point of concurrency.

Non-Concurrent Force System

A force system in which the lines of action of the forces do not meet at a common point of concurrency.

Non-Coplanar and Concurrent Force System

A system in which forces lie in different planes but pass through a single common point, such as forces acting at the top end of an electrical pole.

Parallelogram Law of Forces

A principle stating that two forces $F_1$ and $F_2$ acting at an angle $\phi$ can be replaced by a single resultant force $R = \sqrt{F_1^2 + F_2^2 + 2F_1F_2\cos(\phi)}$.

Triangle Law of Forces

A law stating that if two forces acting at a point are represented in magnitude and direction by two adjacent sides of a triangle taken in order, their resultant is represented by the closing side taken in reverse order.

Polygon Law of Forces

A principle stating that if a number of forces acting simultaneously on a particle are represented in magnitude and direction by the sides of a polygon taken in order, their resultant is represented by the closing side in opposite order.

Equilibrant

A single force that balances a given system of forces, equal in magnitude but opposite in direction to the resultant force.