Name: free-body diagrams for force analysis
Uploaded: 2023-09-22T11:49:20.000Z
Duration: 1 min 28 s
Channel: JoVE

K12 Standards

Next Generation Science Standards

High School

Physical Science

motion-and-stability-forces-and-interactions

Motion and Stability: Forces and Interactions

HS-PS2-3

Free-body Diagram

La représentation visuelle de toutes les forces agissant sur la particule est appelée diagramme de corps libre ou diagramme de force. Il transforme des problèmes complexes en représentations simples.
Dans un diagramme à corps libre, la direction des flèches indique la direction des forces, tandis que la longueur des flèches représente l'amplitude des forces.
Prenons l’exemple d’un chariot stationnaire sur lequel sont empilées deux boîtes en carton.
Ici, les deux systèmes d’intérêt, la case un et la case deux, peuvent être considérés comme des systèmes isolés et peuvent être représentés à l’aide d’un diagramme à corps libre sous la forme d’un simple contour ou d’un point.
Les forces agissant sur la première case sont la force gravitationnelle, qui définit son poids, et la force normale de contrepoids due à la deuxième case.
De même, les forces exercées sur la boîte deux sont son propre poids, la force normale due au chariot et le poids de la première boîte.
Les diagrammes à corps libre jouent un rôle essentiel dans le processus de résolution de problèmes en tant que transition d’une situation physique spécifique à une équation mathématique abstraite en mécanique.

<ol>
	<li>Hibbeler, R.C. (2016). Génie mécanique \u2012 Statique et dynamique. Hoboken, New Jersey : Pearson Prentice Hall. page 88</li>
	<li>Bière, F.P. ; Johnston, E.R. ; Mazurek, D.F ; Cromwell, P.J. et Self, B.P. (2019). Mécanique vectorielle pour les ingénieurs \u2012 Statique et dynamique. New York : McGraw-Hill. p. 170 et 171</li>
</ol>

diagramme des forces

En mécanique, comprendre le mouvement des objets est essentiel, et un outil qui aide à résoudre ce problème est le diagramme des forces. C'est une représentation graphique simple mais puissante qui représente de manière concise toutes les forces agissant sur un objet. Un diagramme des forces peut représenter un objet stationnaire ou en mouvement, et est utilisé en mécanique pour expliquer la cause du mouvement d'un objet. Un diagramme des forces transforme un problème complexe en une représentation simple, ce qui facilite la compréhension des forces essentielles agissant sur un objet, conduisant à une équation mathématique. Dans de nombreux cas, l'équation serait extrêmement complexe à déduire sans utiliser de diagrammes des forces. Pour réaliser un diagramme des forces, commencez par sélectionner l'objet ou le système à inspecter, en l'isolant de son environnement, puis dessinez-le sous forme d'un point ou d'un simple contour. Ensuite, représentez toutes les forces externes essentielles agissant sur l'objet ou le système d'intérêt avec des flèches. La direction des flèches représente la direction de la force, tandis que la longueur des flèches représente l'intensité de la force. Il est important de noter que dans un diagramme des forces, la vitesse et l'accélération ne sont pas représentées, mais peuvent être déduites des forces appliquées sur l'objet. Certains types courants de forces qui peuvent être représentées dans un diagramme des forces comprennent le poids, la force normale, la tension, la friction et la force appliquée. Le poids fait référence à la force de gravité agissant sur l'objet, généralement représentée par une flèche pointant vers le bas. La force normale est la force entre deux objets lorsqu'ils entrent en contact les uns avec les autres ; cette force agit dans la direction opposée au poids de l'objet. La tension est généralement représentée par une flèche pointant loin de l'objet dans la direction de la force, et la friction est la force qui résiste au glissement entre les surfaces. Enfin, la force appliquée fait référence à la force appliquée à l'objet par un agent externe, tel qu'une poussée ou une traction. Les forces appliquées sont représentées par une flèche pointant dans la direction de la force. Considérez un chariot stationnaire, sur lequel deux boîtes en carton sont empilées. Les deux systèmes d'intérêt, la boîte un et la boîte deux, peuvent être considérés comme des systèmes isolés et peuvent être représentés à l'aide d'un diagramme des forces. Les forces agissant sur la boîte un sont la force gravitationnelle, qui définit son poids, et la force normale de contrebalancement due à la boîte deux. De même, les forces sur la boîte deux sont son poids, la force normale due au chariot, et le poids de la boîte un.

Diagramme des forces

En mécanique, il est essentiel de comprendre le mouvement des objets, et un outil qui aide à résoudre ce problème est le diagramme du corps libre. C’est un jeu simple mais ...

Education

Enseignement

JoVE Core

Mechanical Engineering

Génie mécanique

Unit 1

Unité 1

Equilibrium of a Particle

Équilibre d'une particule

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

free-body diagrams for force analysis

Free-body diagrams help analyze the forces acting on an object in mechanics. They give a simple picture of a stationary or moving object and show why it moves the way it does. By turning a complex situation into a clear sketch, they make it easier to write the equation needed to solve the problem.

To draw a free-body diagram, first choose the object or system you want to study. Then isolate it from its surroundings and draw it as a dot or a simple outline. Add arrows for every important external force. The direction of each arrow shows the direction of the force, and the length shows its size.

A free-body diagram does not show velocity or acceleration. Those quantities are not drawn on the diagram, but they can be inferred from the forces acting on the object. Common forces include weight, normal force, tension, friction, and applied force. Weight is the force of gravity and is usually shown with an arrow pointing downward.

Normal force is the contact force between two objects touching each other. It acts in the direction opposite to the object's weight in many situations. Tension is usually drawn as an arrow away from the object and along the direction of the pull. Friction resists sliding between surfaces. Applied force is an outside push or pull, and it is shown with an arrow in the direction of that force.

A stationary trolley with two cardboard boxes stacked on it gives a clear example. Box one and box two can each be treated as separate isolated systems and shown with their own free-body diagrams. For box one, the forces are gravitational force and the balancing normal force from box two. For box two, the forces are its weight, the normal force from the trolley, and the weight of box one.

Free-Body Diagrams for Force Analysis

equilibrium conditions for a particle

Balanced Forces and Torque in Equilibrium

Equilibrium depends on balanced forces and balanced torque. An object in equilibrium is either at rest or moving with a constant velocity. These two cases are called static equilibrium and dynamic equilibrium. Static equilibrium means the object is not moving. Dynamic equilibrium means the object is moving, but its velocity stays constant. In both cases, the forces acting on the object must balance each other. Different forces can add, subtract, or cancel each other out. When the vector sum...

free-body diagram

Free-body diagrams help analyze the forces acting on an object in mechanics. They give a simple picture of a stationary or moving object and show why it moves the way it does. By turning a complex situation into a clear sketch, they make it easier to write the equation needed to solve the problem. To draw a free-body diagram, first choose the object or system you want to study. Then isolate it from its surroundings and draw it as a dot or a simple outline. Add arrows for every important...

steps for free-body diagram

Free-Body Diagram for Two-Block Motion

A free-body diagram helps analyze two-block motion in mechanics. It shows the forces acting on a system so the net force can be found and the acceleration can be calculated. The example in this lesson uses two blocks linked by a massless string over a frictionless pulley. Block 1 moves across a table while block 2 falls under gravity. The two blocks are treated as one isolated system. External forces are then identified and drawn as vector arrows on the diagram. For block 1, the forces...

free-body diagrams: problem solving

Free-Body Diagrams on Inclined Planes

Free-body diagrams help show the forces acting on an object on an inclined plane. A free-body diagram is a simple drawing that focuses only on the object or system being studied. It leaves out extra details so the force problem is easier to analyze and solve. For an example, a 10 kg block is released on a ramp that is 30° to the horizontal. The coefficient of friction is 0.2. The diagram for this block includes the weight from gravity, the normal force, and the frictional force. These are the...

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Coplanar forces act on an object in the same plane. To analyze this kind of system, each force is resolved into x and y components using Cartesian vector form and vector algebra. This makes it possible to test whether the object is in equilibrium. A coplanar system is in equilibrium when the resultant force is zero. That means the sum of the forces in each direction must also be zero. If the forces do not balance, the object is not in equilibrium and will accelerate in the direction of the net...

categories of equilibrium

Types of Equilibrium in Forces

Equilibrium in physics describes how forces act on a body so it stays still or moves at a constant speed. In two-dimensional force systems, equilibrium can be grouped into several categories based on how the forces are arranged. Collinear equilibrium is the simplest case. The forces act along one straight line, so only one force equation is needed in the direction of those forces. The other equations are already satisfied. Coplanar concurrent equilibrium is another category. In this case, all...

key terms and concepts

Learn how free-body diagrams show weight, normal force, tension, friction, and applied force. See how isolating an object simplifies force analysis in mechanics.

Free-Body Diagrams for Force Analysis | JoVE K12

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HS-PS2-6

Free-Body Diagrams for Force Analysis

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