4 - Equilibrium in 2D Flashcards
What are the two base equilibrium equations?
R = Sigma * F = 0 M = Sigma * M = 0
What is equilibrium?
Equilibrium is the state in which all the forces on a body are exactly in balance so that the body does not move. When all the forces that act on an object are balanced, then the object is said to be in a state of equilibrium.
What is a mechanical system?
A system which can be defined as a body or group of bodies that can be conceptually isolated from all other bodies.
A system may be a single body or a combination of connected bodies. The bodies may be rigid or nonrigid. The system may also be an identifiable fluid mass, either liquid or gas, or a combination of fluids and solids.
What is a free body diagram?
A diagrammatic representation of the isolated system which is treated as a single body. The diagram shows all forces applied to the system by mechanical contact with other bodies, which are imagined to be removed.
What is the single most important step in solving problems in mechanics?
Free-body diagram.
How can forces be applied?
Either by direct physical contact or by remote action.
How do we apply Newton’s Third Law in modelling the action of forces?
The force exerted on a body in question by a contacting or supporting member is always in the sense to oppose the movement of the isolated body which would occur if the contacting or supporting body were removed.
How do you model the force on a flexible cable, belt, chain, or rope?
Force exerted by a flexible cable is always a tension away from the body in the direction of the cable.
How do you model the force on a smooth surface?
Contact force is compressive and is normal to the surface.
How do you model the force on a rough surface?
Rough surfaces are capable of supporting a tangential component F (frictional force) as well as a normal component N of the resultant contact force R.
How do you model the force on a roller support?
Roller, rocker, or ball support transmits a compressive force normal to the supporting surface.
How do you model the force on a freely sliding guide?
Collar or slider free to move along smooth guides; can support force normal to guide only.
How do you model the force on a pin connection?
A freely hinged pin connection is capable of supporting a force in any direction in the plane normal to the pin axis. We may either show two components Rx and Ry or a magnitude R and direction theta. A pin not free to turn also supports a couple M.
How do you model the force on built-in or fixed support?
A built-in or fixed support is capable of supporting an axial force F, a transverse force V (shear force), and a couple M (bending moment) to prevent rotation.
How do you model the force of gravitational attraction?
The resultant of gravitational attraction on all elements of a body of mass m is the weight, W = mg, and acts towards the centre of the earth through the centre of gravity G.
