Name: rigid body force balance in equilibrium
Uploaded: 2023-09-22T11:49:22.000Z
Duration: 1 min 28 s
Channel: JoVE

Un corpo rigido non subisce alcuna deformazione sotto l'influenza di forze esterne.
Si consideri una giostra soggetta a una forza esterna F a una distanza radiale perpendicolare r, che risulta nel momento di una forza attorno al punto O.
Se più forze agiscono sulla giostra, la condizione di equilibrio si ottiene quando la somma di tutte le forze esterne che agiscono su di essa è zero.
L'altra condizione di equilibrio afferma che la somma di tutti i momenti attorno al punto O deve essere uguale a zero.
Quando il momento è misurato nel punto A, può essere espresso come la somma del momento nel punto O e il prodotto incrociato della distanza perpendicolare e della forza applicata.
Queste condizioni fanno sì che il corpo non subisca alcun movimento traslazionale o rotatorio in equilibrio statico.
Qui vengono considerate solo le forze esterne poiché le forze interne all'interno del corpo rigido hanno la stessa grandezza e agiscono in direzioni opposte, annullandosi a vicenda a causa della terza legge del moto di Newton.

<ol>
	<li>Birra, F.P.; Johnston, E.R.; Mazurek, D.F; Cromwell, P.J. e Self, B.P. (2019). Meccanica vettoriale per ingegneri \u2012 Statica e dinamica. New York: McGraw-Hill. pagine 170</li>
</ol>

condizioni di equilibrio

Conditions of Equilibrium

L'equilibrio si riferisce ad uno stato in cui un corpo rigido non è soggetto ad alcun moto di traslazione o rotazione. Questo stato viene raggiunto quando la forza e la coppia che agiscono su un corpo rigido sono uguali a zero. Quando il sistema di forze esterne produce un effetto netto equivalente a zero, il corpo rigido è considerato in equilibrio.

Le forze interne non vengono prese in considerazione per le condizioni di equilibrio, perché si verificano a coppie uguali ed opposte all'interno del corpo, annullandosi reciproocamente. Di conseguenza, queste forze interne non contribuiscono al moto complessivo o al cambiamento del moto del corpo rigido. L'equilibrio è determinato dal bilanciamento delle forze esterne e dei momenti che agiscono sul corpo, poiché sono responsabili della causa del moto di traslazione o rotazione.

Le condizioni necessarie e sufficienti per l'equilibrio, possono essere determinate impostando la forza risultante e il momento come uguali a zero. Inoltre, le equazioni vettoriali possono essere sostituite con sei equazioni scalari risolvendo ciascuna forza e momento nelle loro componenti rettangolari. Ciò implica che le componenti delle forze esterne nelle direzioni x, y e z sono bilanciate e anche i momenti delle forze esterne rispetto agli assi x, y e z sono bilanciati. Se un corpo rigido è in equilibrio, il sistema di forze esterne non produce alcun moto di traslazione o rotazione nel corpo.

Per scrivere le equazioni di equilibrio per un corpo rigido, si identificano prima tutte le forze che agiscono sul corpo e si disegna il corrispondente diagramma di corpo libero. Oltre alle forze applicate ad una struttura, si considerano le reazioni esercitate sulla struttura dai suoi supporti. Identificare correttamente ogni reazione può aiutare a risolvere le forze e le reazioni sconosciute.

La conoscenza delle condizioni di equilibrio è cruciale nell'analisi dei problemi legati ai corpi rigidi. Determinando le forze e le reazioni sconosciute, e utilizzando le condizioni necessarie e sufficienti per l'equilibrio, è possibile prevedere il comportamento dei corpi rigidi.

Condizioni di equilibrio

L'equilibrio si riferisce a uno stato in cui un corpo rigido non è soggetto ad alcun movimento traslazionale o rotatorio. Questo stato si ottiene quando la forza e ...

Education

Didattica

JoVE Core

Mechanical Engineering

Ingegneria Meccanica

Unit 1

Unità 1

Equilibrium of a Rigid Body

Equilibrio di un corpo rigido

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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 external forces and moments determine whether the body stays balanced. These are the forces that can cause translation or rotation. The necessary and sufficient conditions for equilibrium are found by setting the resultant force and the resultant moment equal to zero.

The vector equations for equilibrium can also be written as six scalar equations. Each force and moment is resolved into rectangular components. This means the external force components in the x, y, and z directions must balance, and the moments about the x, y, and z axes must also balance.

To write equilibrium equations for a rigid body, first identify all forces acting on it. Then draw a free-body diagram. The reactions from supports must also be included. Correctly identifying each reaction helps solve unknown forces and reactions in structures.

Rigid Body Force Balance in Equilibrium

conditions of 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

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 rigid body equilibrium is determined by balanced external forces and moments, free-body diagrams, and support reactions in high school physics.

Rigid Body Force Balance in Equilibrium | 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

Rigid Body Force Balance in Equilibrium

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