Name: forces inside a body and balance
Uploaded: 2023-09-22T11:49:22.000Z
Duration: 1 min 25 s
Channel: JoVE

Les forces internes sont générées à l’intérieur d’un corps en raison de l’interaction entre ses particules. Ces forces comprennent la tension, la compression et le cisaillement. 
Les forces internes existent en paires colinéaires d’amplitude égale mais de directions opposées. Ils s'annulent entre toutes les parties connectées, ce qui entraîne l'équilibre du corps.
Le poids d'un corps est une force externe représentée par une seule force résultante agissant à travers le centre de gravité du corps.
C’est le point où un corps s’équilibre, pourvu qu’aucune force extérieure n’agisse sur lui.
Un corps symétrique ou uniforme a son centre de gravité à son centre géométrique. Cependant, pour un corps irrégulier ou non uniforme, il est décentré vers le côté le plus lourd.
Considérons une poutre attachée à une grue au centre, avec des charges connectées à ses extrémités. Si la charge d’un côté devient lourde, le centre de gravité s’éloignera de l’axe de la poutre, ce qui peut provoquer un basculement.
Le centre de gravité doit être identifié pour assurer la stabilité, et le crochet de levage doit être placé directement au-dessus.

<ol>
	<li>Russell C. Hibbeler. (2016). Mécanique de l’ingénierie : statique et dynamique. Pearson. Pages 212.</li>
</ol>

forces internes et centre de gravité

Internal Forces and Center of Gravity

Les forces internes et le centre de gravité sont des concepts fondamentaux en mécanique, jouant un rôle crucial dans la compréhension du comportement et de la stabilité des structures et des objets dans différentes conditions. Une compréhension exhaustive de ces principes est essentielle pour les ingénieurs, les architectes et les concepteurs afin de créer des systèmes sûrs et efficaces. Les forces internes sont générées à l'intérieur d'un corps en raison de l'interaction entre ses particules. Ces forces peuvent être classées en forces de tension, de compression et de cisaillement. Ces forces internes existent par paires colinéaires avec une magnitude égale mais des directions opposées. Elles s'annulent entre toutes les parties connectées, maintenant l'équilibre du corps. Le poids d'un corps est une force externe représentée par une seule force résultante agissant à travers le centre de gravité du corps. Le centre de gravité est le point où un corps s'équilibre lorsqu'aucune force externe n'agit sur lui. Le centre de gravité se situe au centre géométrique pour les corps symétriques ou uniformes. Cependant, le centre de gravité peut être déplacé vers le côté le plus lourd pour les corps irréguliers ou non uniformes. La compréhension des forces internes et du centre de gravité est cruciale pour analyser et maintenir la stabilité et l'équilibre de différentes structures et objets. Par exemple, en génie civil, ces principes sont utilisés pour concevoir des ponts, des bâtiments et d'autres infrastructures capables de résister à des forces externes telles que le vent, les tremblements de terre et les charges de circulation. En génie mécanique, la connaissance des forces internes et du centre de gravité est appliquée à la conception de machines, de véhicules et d'autres systèmes mécaniques capables de fonctionner en toute sécurité et efficacement sous différentes charges et conditions. En génie aérospatial, déterminer avec précision le centre de gravité des avions et des engins spatiaux est vital pour assurer la stabilité et le contrôle en vol. Un déplacement du centre de gravité peut avoir de graves conséquences sur les performances et la sécurité de ces véhicules.

Forces internes et centre de gravité

Les forces internes et le centre de gravité sont des concepts fondamentaux en mécanique, jouant un rôle crucial dans la compréhension du comportement et de la stabilité ...

Education

Enseignement

JoVE Core

Mechanical Engineering

Génie mécanique

Unit 1

Unité 1

Equilibrium of a Rigid Body

Équilibre d'un corps rigide

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

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 equilibrium.

A body’s weight is an external force. It is shown as one resultant force acting through the center of gravity. The center of gravity is the point where a body balances when no external force acts on it. For symmetrical or uniform bodies, this point is at the geometric center. For irregular or non-uniform bodies, it may shift toward the heavier side.

These ideas are important in civil engineering, mechanical engineering, and aerospace engineering. Engineers use them to design bridges, buildings, machines, vehicles, aircraft, and spacecraft that can handle wind, earthquakes, traffic loads, and other forces. If the center of gravity changes, the stability and safety of an aircraft or spacecraft can be affected.

Forces Inside a Body and Balance

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

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

equations-of-equilibrium-in-three-dimensions

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.

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 internal forces and the center of gravity affect balance, stability, and equilibrium in structures, machines, and vehicles.

Forces Inside a Body and Balance | 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

Forces Inside a Body and Balance

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