1.1 Fundamentalconceptsin statics二、Forcel.Concept:the mechanicalinteraction of bodies is caused by force2.Effects of forces:1motion(externaleffect)②deformation(internaleffect)3.The three elements: magnitude,direction and point ofapplicationFBAccording to the action point, the forceAcan be divided into distributed force andconcentrated force.The force can be expressed as a vector. As shown in the figure, the modulus ofthe vectorrepresents the force with a certain scale; The azimuth and direction ofthe vectorindicate the direction ofthe force; The startingpoint (or end point)ofa vectorindicates the pointat which the force is applied.International unit of force:kgm/ s'or Newton(Mand kilonewton(KN)
2 kgm/s 二、Force International unit of force： or Newton(N)and kilonewton(KN) 1.Concept:the mechanical interaction of bodies is caused by force. 2. Effects of forces： ①motion(external effect) ②deformation(internal effect) 3. The three elements：magnitude,direction and point of application The force can be expressed as a vector. As shown in the figure, the modulus of the vector represents the force with a certain scale; The azimuth and direction of the vector indicate the direction of the force; The starting point (or end point) of a vector indicates the point at which the force is applied. F A B According to the action point, the force can be divided into distributed force and concentrated force. 1.1 Fundamental concepts in statics
1.1 Fundamentalconceptsin statics三、ForcesystemForce system-A group of forces acting on a bodyBalanced force system: If a body subjected to a force system is inequilibrium state.Equivalent substitution: The substitution of one force systemwith another force system equivalent to it.Simplification of force systems:A complex force system isequivalently replaced with a simple force system.Resultant: If a force system can be equivalently replaced by aforce, theforceis called the resultant.System of equilibrium: A system of forces acting on a body thatkeeps the bodyin balanceis calleda system of equilibrium.Theconditions that the force system satisfies are called eguilibriumconditions
Balanced force system：If a body subjected to a force system is in equilibrium state. Equivalent substitution：The substitution of one force system with another force system equivalent to it. Simplification of force systems：A complex force system is equivalently replaced with a simple force system. Resultant：If a force system can be equivalently replaced by a force, the force is called the resultant. System of equilibrium：A system of forces acting on a body that keeps the body in balance is called a system of equilibrium.The conditions that the force system satisfies are called equilibrium conditions. 三、Force system Force system——A group of forces acting on a body. 1.1 Fundamental concepts in statics
1.1 Fundamentalconceptsin staticsForcesvstem classification:According to the action line of force distribution: planeforcesystem,spaceforce systemAccording to the action line relation of force: confluenceforce system, parallel force system, arbitrary force system
Force system classification： According to the action line of force distribution：plane force system, space force system According to the action line relation of force：confluence force system, parallel force system, arbitrary force system 1.1 Fundamental concepts in statics
1.2PrinciplesofstaticsAioThd distictidinbetfeen bxlamse theorems, and lawsTwo forces acting on a rigid body balance the necessary andFisufficient conditions are as follows::the two forces are equal in magnitude, opposite inRigid bodydirection, and along the same straight line.RInstruction:1, Equilibrium conditions for the simplest force system 。2, It is a necessary and sufficient condition for rigid bodies and anecessary but not sufficient condition for deformed bodies.(DE)FiFF2FDeformable body(rope)Multi-body
Axiom 1 Axiom of two-force balance Two forces acting on a rigid body balance the necessary and sufficient conditions are as follows: ： 2、It is a necessary and sufficient condition for rigid bodies and a necessary but not sufficient condition for deformed bodies.(DE) Instruction： 1、Equilibrium conditions for the simplest force system。 the two forces are equal in magnitude, opposite in direction, and along the same straight line. 1.2 Principles of statics ？The distinction between axioms, theorems, and laws Rigid body Deformable body(rope) Multi-body
1.2Principles of statics3, Application: Two-force member:Arigid body balanced byonly two forces.Imn-forrebodyTwo-forcebarFiF
3、Application：Two-force member：A rigid body balanced by only two forces. Two-force bar 1.2 Principles of statics