Name: work in force and motion
Uploaded: 2023-09-22T11:49:36.000Z
Duration: 1 min 14 s
Channel: JoVE

Le travail se produit lorsqu’une force agissant sur un objet le déplace. Il est égal au produit de la composante scalaire de la force le long de la direction du déplacement.
Mathématiquement, le travail peut être donné comme le produit scalaire de la force appliquée et du déplacement de l’objet.
L’unité SI de travail est le joule. Un joule est le travail effectué lorsqu’une force d’un newton déplace un objet d’un mètre.
Comme le travail est une grandeur scalaire, son intensité peut être positive, négative ou nulle selon la direction de la force par rapport au déplacement.

Prenons l’exemple d’une grue soulevant une charge vers le haut. Ici, la force appliquée et les vecteurs de déplacement sont alignés dans la même direction, de sorte que le travail effectué est positif.

Dans un autre exemple, lorsque les freins sont appliqués à une voiture en mouvement, la force de freinage agit dans la direction opposée au mouvement de la voiture. Ici, le travail effectué est négatif.

Une poulie sans friction soulevant une charge à travers une corde inextensible sans masse ne fait aucun travail car la force et le déplacement sont perpendiculaires.

<ol>
	<li>Hibbeler, R.C. (2016). Mécanique du génie : Statique. Quatorzième édition, New Jersey : Pearson. Section 11.1, p. 581 et 582.</li>
	<li>Meriam, J.L., Kraige, L.G. et Bolton, J.N. (2016). Mécanique de l’ingénierie : statique et dynamique. Huitième édition, Singapour : John Wiley & Sons. Section 7.2, p. 392 et 393.</li>
	<li>Beer, F.P., Johnston, E.R., Mazurek, D.F., Cornwell, P.J. et Self, B.P. (2016). Mécanique vectorielle pour les ingénieurs. Onzième édition, New York : McGraw-Hill Education. Section 10.1A, p. 575.</li>
</ol>

le travail

Le travail est un concept fondamental de l'ingénierie mécanique et a de nombreuses applications. Comprendre comment calculer le travail et les différents types de travail peut nous aider à mieux comprendre les processus physiques et à fournir des informations sur les problèmes complexes. Le travail est défini comme le résultat d'une force agissant sur un objet, le faisant se déplacer le long de la ligne d'action de la force. Il est également défini comme le processus de transfert d'énergie par l'application d'une force sur un objet, ce qui entraîne son déplacement. Ce transfert d'énergie est responsable du changement de mouvement ou de position de l'objet. Le travail peut être écrit comme le produit de la force et de la composante du déplacement dans la même direction, ou alternativement écrit comme le produit scalaire de la force appliquée et du déplacement de l'objet. Le système international considère un joule comme son unité, ce qui équivaut à effectuer un newton de force sur un mètre de déplacement. Le type de travail fait sur un objet dépend de la direction de la force par rapport au déplacement. Si la force appliquée et le déplacement sont parallèles l'un à l'autre, le travail effectué est positif et s'ils sont antiparallèles, le travail effectué est négatif. Lorsque la force appliquée et le déplacement sont perpendiculaires l'un à l'autre, le travail effectué est nul. Un exemple de travail positif est lorsqu’une grue soulève une lourde charge – en exerçant une force vers le haut sur la charge, elle se déplace vers le haut par rapport au niveau du sol. Le travail négatif se produit, par exemple, lorsque les freins sont appliqués à une voiture en mouvement – les roues exercent une force opposée à son mouvement, ce qui entraîne un travail négatif effectué sur elle. Certaines forces, telles que celles agissant sur des points fixes ou perpendiculaires au déplacement, ne font aucun travail. Des exemples incluent la réaction au niveau d'une goupille sans frottement lorsque le corps supporté tourne autour d'elle, la force de réaction agissant sur un corps se déplaçant sur une surface sans frottement, etc. Cependant, les forces qui font un travail incluent le poids d'un corps et la force de frottement agissant sur un corps se déplaçant sur une surface rugueuse. Dans certains cas, la somme du travail effectué par plusieurs forces est nulle. Par exemple, deux corps rigides reliés par une goupille sans frottement nécessitent des forces égales mais opposées pour se déplacer, de sorte que leur travail combiné est nul. De même, deux blocs reliés par une corde extensible ont des forces de tension de même magnitude mais de signes opposés, ce qui résulte en un travail nul. Globalement, comprendre quelles forces produisent du travail et comment calculer le travail peut fournir des informations utiles sur des problèmes physiques complexes et nous permettre de gérer ces processus efficacement pour obtenir les résultats souhaités.

Le travail

Le travail est un concept fondamental de l’ingénierie mécanique et a de nombreuses applications. Comprendre comment le travail est calculé et les différents types de travail ...

Education

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Virtual Work

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KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

Work

work in force and motion

Work connects force, motion, and energy in mechanics. It happens when a force acts on an object and the object moves along the line of action of that force. Work can also be described as energy transfer caused by applying a force, which leads to a change in the object’s motion or position.

Work is calculated as the force multiplied by the part of the displacement in the same direction as the force. It can also be written as the dot product of the applied force and the object’s displacement. In the SI system, the unit of work is the joule. One joule is equal to one newton of force acting over one meter of displacement.

The direction of the force compared with the displacement tells us the type of work done. When the force and displacement are parallel, the work is positive. When they are anti-parallel, the work is negative. When the force and displacement are perpendicular, the work is zero.

A crane lifting a heavy load is an example of positive work. The crane applies an upward force, and the load moves upward. Brakes on a moving car show negative work. The wheels exert a force that opposes motion, so work is done against the car’s movement.

Some forces do no work. This includes forces acting at fixed points or forces perpendicular to displacement. Examples include the reaction at a frictionless pin when a body rotates about it, and the reaction force on a body moving on a frictionless surface. Forces that do work include the weight of a body and friction acting on a body moving on a rough surface.

In some systems, the total work done by multiple forces is zero. Two rigid bodies connected by a frictionless pin need equal and opposite forces for motion, so their combined work is zero. The same idea applies to two blocks connected by an extensible cord, where the tension forces have equal magnitude but opposite signs. Knowing which forces produce work helps explain physical processes and solve mechanical problems.

Work in Force and Motion

work

Work connects force, motion, and energy in mechanics. It happens when a force acts on an object and the object moves along the line of action of that force. Work can also be described as energy transfer caused by applying a force, which leads to a change in the object’s motion or position. Work is calculated as the force multiplied by the part of the displacement in the same direction as the force. It can also be written as the dot product of the applied force and the object’s displacement. In...

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key terms and concepts

Learn how work is calculated from force and displacement, why it can be positive, negative, or zero, and see real examples from cranes and brakes.

Work in Force and Motion | 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

Work in Force and Motion

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