Topic 5 ( EQUILIBRIUM OF A RIGID BODY ) Flashcards
Keywords: Zero forces, zero moments, balance
Definition: A rigid body is in equilibrium when the resultant forces and resultant moments acting on it are zero.
Equilibrium
ΣFx = 0, ΣFy = 0, ΣM = 0
Equilibrium Conditions
Keywords: External, known forces
Definition: Forces exerted on a body by external agents, such as weights, wind, or tension in a cable.
Applied Forces
Keywords: Support, resistance, unknown forces
Definition: Forces exerted by supports or connections to resist motion. Examples include normal forces, tension, and friction.
Reactive Force
Types of Supports
Pin, roller, fixed, reaction types
Restricts movement in two directions (horizontal and vertical forces).
Pin Support:
Restricts movement in one direction (vertical or horizontal force only).
Roller Support
Restricts all movement and rotation (horizontal, vertical, and moment reactions).
Fixed Support
Rotation, force × distance
Moment
Keywords: Solvable, equations = unknowns
Definition: A structure or system where the number of equilibrium equations equals the number of unknowns, allowing it to be solved using only equilibrium conditions.
Statically Determinate
Keywords: Excess unknowns, requires other methods
Definition: A structure or system where the number of unknowns exceeds the equilibrium equations, requiring additional methods (e.g., compatibility equations).
Statically Indeterminate
Keywords: 2D, coplanar forces
Definition: The geometric plane in which all forces acting on a body lie.
Plane of Action
Keywords: Coplanar, concurrent, parallel
Definition: A group of forces acting on a rigid body, categorized as concurrent, parallel, or non-concurrent/non-parallel.
Force System
is a simplified representation of an object or system, showing all the forces acting on it. It’s a critical tool in mechanics, especially in statics and dynamics, to analyze and solve problems involving forces and moments.
Free Body Diagram (FBD)
An _____ is any external force exerted on an object by another object, person, or system. It’s what initiates motion, deformation, or some other effect.
eX. Pushing a box across the floor.
A person pulling on a rope.
The thrust from an engine.
applied force
A ____ is a force that opposes or reacts to an applied force, according to Newton’s Third Law (“For every action, there is an equal and opposite reaction”).
Ex. A table exerting an upward force on a book placed on it (normal force).
The ground pushing back when you step on it.
The tension in a rope countering the pull of gravity.
reactive force
Examples of ____ include normal force, friction, and tension.
reactive forces
_____ Force comes from an external agent
Applied
___ Force originates due to the response of the object or environment to the applied force.
also acts in the opposite direction of the applied force.
Reactive
_____can only support tensile forces (pulling forces). It cannot resist compressive or bending forces.
flexible cable
____ are often used in problems involving pulleys, hanging loads, suspension bridges, or hoisting systems.
cables
A ___ support is a type of support used in engineering to allow a structure to rest on it while permitting movement in one direction, typically horizontal. It is commonly used in problems involving beams or structures that need flexibility to move or expand due to thermal effects, wind loads, or other factors.
roller
A ___ support only provides one reaction force. This force is perpendicular to the surface the roller rests on (usually vertical), but it does not resist horizontal movement.
roller
The__supports the structure vertically, but it does not prevent it from moving sideways (in the horizontal direction).
roller
A____support is often represented by a circle with a perpendicular arrow pointing upward to indicate the vertical reaction force.
roller
