Name: checking force balance in 3d structures
Uploaded: 2023-09-22T11:49:23.000Z
Duration: 1 min 30 s
Channel: JoVE

Considérons un trépied placé sur un sol ; sa patte est reliée à l’aide d’une rotule en A et l’autre extrémité B est sur le sol.
Lorsque la force résultante et le moment de couple résultant agissant sur la jambe sont nuls, on dit que la jambe est en équilibre et peut être exprimée à l’aide d’équations d’équilibre.
Puisque la jambe est sous l’équilibre, elle satisfait les équations vectorielle et scalaire de l’équilibre.
Selon les équations vectorielles d’équilibre, toutes les forces externes agissant sur la jambe doivent avoir une somme vectorielle de zéro. La somme vectorielle de tous les moments de couple et des moments de toutes les forces autour d’un point doit également être égale à zéro.
Selon les équations scalaires de l’équilibre, si les forces externes sont exprimées sous forme cartésienne, alors la somme de la composante des forces le long des directions respectives doit être nulle.
De même, la sommation scalaire des composantes d’un moment dans les axes x, y et z doit également être nulle.

<ol>
	<li>Hibbeler, R.C. (2016). Génie mécanique \u2012 Statique et dynamique. Hoboken, New Jersey : Pearson Prentice Hall. page 250</li>
</ol>

Équations d'équilibre en trois dimensions

Equations of Equilibrium in Three Dimensions

Lors de l'analyse de structures ou de systèmes au repos, il est nécessaire de s'assurer qu'ils sont en équilibre. C'est là que les équations vectorielles et scalaires d'équilibre entrent en jeu. Ces équations sont cruciales pour garantir qu'une structure est stable et ne s'effondrera pas ou ne se désagrégera pas. Les équations vectorielles et scalaires d'équilibre fournissent un cadre pour analyser les forces agissant sur un corps. Selon les équations vectorielles d'équilibre, la somme vectorielle de toutes les forces externes agissant sur un corps doit être égale à zéro. De plus, la somme vectorielle des moments couples et des moments de toutes les forces autour d'un point doit également être égale à zéro. <img alt="Equation 1" src="/files/ftp_upload/14275/14275_Equation_1v2.svg" style="text-align: center; height: 33px;"> Les équations scalaires d'équilibre stipulent que si les forces externes sont exprimées sous forme cartésienne, alors la somme des composantes des forces le long des directions respectives doit être nulle. <img alt="Equation 2" src="/files/ftp_upload/14275/14275_Equation_2v2.svg" style="text-align: center; height: 55px;"> De même, la sommation scalaire des composantes d'un moment dans les axes x, y et z doit également être nulle. <img alt="Equation 3" src="/files/ftp_upload/14275/14275_Equation_3v2.svg" style="text-align: center; height: 55px;"> Ces équations sont fondamentales en génie mécanique, garantissant la sécurité et la stabilité des structures.

Lors de l’analyse de structures ou de systèmes au repos, il est nécessaire de s’assurer qu’ils sont en équilibre. C’est là que les équations vectorielle et scalaire de ...

equations-of-equilibrium-in-three-dimensions

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checking force balance in 3d structures

Checking force balance in 3D structures is a key step when a system is at rest. The vector and scalar equations of equilibrium are used to test whether a body is stable and will not collapse or fall apart. These equations give a clear way to study the forces acting on a body.

The vector equations of equilibrium require the vector sum of all external forces on a body to equal zero. They also require the vector sum of the couple moments and the moments of all forces about a point to equal zero. A couple moment is a turning effect produced by a pair of forces.

The scalar equations of equilibrium use Cartesian form, which means the forces are written in x, y, and z components. In that form, the sum of the force components along each direction must be zero. The scalar sum of the moment components about the x, y, and z axes must also be zero. These conditions are fundamental in mechanical engineering because they help show that structures are safe and stable.

Checking Force Balance in 3D Structures

conditions of equilibrium

Rigid Body Force Balance in Equilibrium

Rigid body equilibrium depends on a balance of external forces and moments. A rigid body is in equilibrium when it has no translational motion and no rotational motion. This happens when the net force and the net couple acting on the body are both zero. Internal forces are not used when checking equilibrium. These forces act in equal and opposite pairs inside the body, so they cancel each other. Because of that, they do not affect the overall motion or change in motion of the rigid body. The...

support reactions

Types of Structural Supports

Types of structural supports control how a coplanar force system moves and reacts under load. A coplanar force system is a set of forces that all lie in the same plane. The supports create reactions at the point of contact. These reactions help keep a structure stable under external forces. Supports work by stopping translation with an equal and opposite force. They can also stop rotation by applying a couple moment in the opposite direction. In structural design, these reactions are important...

internal forces and center of gravity

Forces Inside a Body and Balance

Internal forces and the center of gravity help explain how objects stay in balance. These mechanics ideas matter for structures, machines, and vehicles that must remain stable under different loads and conditions. Internal forces are created inside a body when its particles interact. They can appear as tension, compression, or shear forces. These forces act in collinear pairs with equal magnitude and opposite direction. Between connected parts, they cancel each other and help keep the body in...

alternative sets of equilibrium equations

alternative-sets-of-equilibrium-equations

Equilibrium Conditions for a Supported Plate

Equilibrium conditions for a supported plate are used to describe when forces and moments balance. In this state, the plate has no net movement and no rotation. Engineers use these equations to study how structures behave under external loads. In many cases, the standard equilibrium equations are enough. But some systems need an alternative set of equations to match the geometry of the support points. A rectangular plate supported at points A, B, and C is one example. For this plate, the...

two force member

Two-Force Body Equilibrium

A two-force body is a rigid body acted on by only two external forces. In equilibrium, those two forces must have the same magnitude, the same line of action, and opposite directions. This balance is what keeps the body at rest. For a plate with forces F1 and F2 applied at points A and B, equilibrium means the sum of moments about any axis is zero. If moments are summed about point A, the moment from F2 must be zero. That means the line of action of F2 must pass through point A. The same idea...

three force member

Solving a Three-Force Member Example

A three-force member is a rigid body acted on by three forces at three points. The forces must have concurrent lines of action. If the forces are parallel, their lines of action stay parallel instead. A dumpster provides the example used here. It is connected to a pin support at point A and to a pin on a hydraulic cylinder at point B. The hydraulic cylinder acts as a two-force member in equilibrium. The dumpster weight acts through the center of gravity, and the support reaction acts at point...

equations of equilibrium in three dimensions

Checking force balance in 3D structures is a key step when a system is at rest. The vector and scalar equations of equilibrium are used to test whether a body is stable and will not collapse or fall apart. These equations give a clear way to study the forces acting on a body. The vector equations of equilibrium require the vector sum of all external forces on a body to equal zero. They also require the vector sum of the couple moments and the moments of all forces about a point to equal zero.

support reactions in three dimensions

3D Support Types for Stability and Motion

Support reactions in three dimensions keep structures stable and in equilibrium. They stop unwanted translation and rotation, so a design can handle external forces safely and work as intended. These reactions are important in many structures and systems. A ball and socket joint is one support that allows free rotation about any axis. It does not provide a moment that resists turning. At the same time, it restricts motion in space with three reaction forces along the three dimensions. A...

constraints and statical determinacy

Constraints in Structural Equilibrium

Constraints in structural engineering control how a body can move and help keep it in mechanical equilibrium. A constraint is a restriction on motion. When the right number of constraints is used, the system can stay balanced with the fewest supports needed. A system with the proper number of supports is called statically determinate. In that case, the unknown reaction forces can be found from equations of equilibrium. These systems are the easiest to analyze and design because the forces can...

key terms and concepts

Learn how vector and scalar equilibrium equations keep 3D structures stable by balancing forces and moments in x, y, and z directions.

Checking Force Balance in 3D Structures | JoVE K12

JoVE Core Mechanical Engineering offers concise, easy-to-understand animated videos covering key topics such as equilibrium, forces, truss analysis, and structural mechanics. Explore their real-world applications, and witness these concepts in action through scientist-led experiments.

mechanical engineering

Checking Force Balance in 3D Structures

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