Name: screw jack force and friction analysis
Uploaded: 2023-09-22T11:49:29.000Z
Duration: 1 min 21 s
Channel: JoVE

Considérez un vérin à vis à filetage carré. L’application d’une force sur sa poignée entraîne un moment de torsion, qui provoque un mouvement imminent de la vis vers le haut. Ceci est réalisé en surmontant le frottement statique entre les filetages de la vis et du cric.
Considérez le fil complètement effiloché comme un bloc en contact avec la rainure du cric et dessinez son schéma de corps libre.
Le moment de torsion produit une force horizontale qui pousse le filetage mobile vers le haut de l’inclinaison fixe du filetage du vérin, et la charge applique une force axiale sur le fil.
La rainure exerce une force de réaction sur le filetage de la vis. Cette réaction a des composantes normales et de friction, qui sont liées par le coefficient de frottement.
L’angle de frottement statique pour un mouvement imminent est égal à l’inverse du coefficient de frottement.
Maintenant, appliquez les équations d’équilibre pour les forces le long des axes horizontal et vertical.
En réarrangeant les équations en fonction de la force de réaction et en les égalisant, on détermine l’équation d’équilibre du moment pour le mouvement imminent vers le haut.

<ol>
	<li>Hibbeler, R.C. (2016). Mécanique du génie : Statique. Quatorzième édition, New Jersey : Pearson. P. 432 et 433.</li>
	<li>Meriam, J.L., Kraige, L.G. et Bolten, J.N. (2016). Mécanique de l’ingénierie : statique et dynamique. Huitième édition, Singapour : John Wiley & Sons. P. 355 et 356.</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. p. 451.</li>
</ol>

mouvement imminent vers le haut

Un vérin à vis filetée carrée est un dispositif mécanique largement utilisé pour soulever de lourdes charges ou appliquer une force considérable. Son fonctionnement est basé sur la conversion de la force appliquée sur sa poignée en un moment de torsion, provoquant le mouvement imminent vers le haut de la vis. Ce mouvement est réalisé en surmontant la friction statique entre les filets de la vis et le vérin. Pour mieux comprendre le fonctionnement d'un vérin à vis, considérez le filet complètement déroulé comme un bloc en contact avec la rainure du vérin. En dressant un diagramme des forces agissant sur ce scénario, nous pouvons analyser les forces agissant sur le système. <img alt="Figure 1" src="/files/ftp_upload/14319/14319_PT_Figure_1v2.svg" style="text-align: center; height: 300px;"> Le moment de torsion produit par la force appliquée sur la poignée génère une force horizontale qui pousse le filet mobile vers le haut de l'inclinaison fixe du filet du vérin. Simultanément, la charge soulevée applique une force axiale sur le filet. La rainure du vérin exerce une force de réaction sur le filet de la vis. Cette force de réaction comprend à la fois des composantes normales et de friction, qui sont liées par le coefficient de friction. L'angle de la friction statique pour le mouvement imminent peut être déterminé en trouvant la tangente inverse du coefficient de friction. <img alt="Equation 1" src="/files/ftp_upload/14319/14319_PT_Equation_1.png" style="text-align: center; height: 18px;"> Avec ces informations, appliquez les équations d'équilibre pour les forces le long des axes horizontal et vertical. <img alt="Equation 2" src="/files/ftp_upload/14319/14319_PT_Equation_2v2.svg" style="text-align: center; height: 28px;"> <img alt="Equation 3" src="/files/ftp_upload/14319/14319_PT_Equation_3v2.svg" style="text-align: center; height: 13px;"> Ces équations permettent l'analyse de la relation entre la force appliquée, les forces de réaction et le mouvement résultant du vérin à vis. En réarrangeant les équations en termes de la force de réaction et en les égalant, on obtient l'équation d'équilibre du moment pour le mouvement imminent vers le haut. <img alt="Equation 4" src="/files/ftp_upload/14319/14319_PT_Equation_4v2.svg" style="text-align: center; height: 13px;"> En résolvant cette équation d'équilibre du moment, on peut déterminer la force minimale requise sur la poignée pour initier le mouvement vers le haut du vérin à vis. Ce calcul permet d'optimiser la conception et le fonctionnement du vérin à vis pour diverses applications, en garantissant qu'il peut soulever efficacement des charges lourdes ou appliquer de grandes forces selon les besoins.

Mouvement imminent vers le haut

Un vérin à vis à filetage carré est un dispositif mécanique largement utilisé pour soulever des charges lourdes ou appliquer une force considérable. Son fonctionnement est basé sur...

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Mechanical Engineering

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Unit 1

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Friction

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Upward Impending Motion

screw jack force and friction analysis

A square-threaded screw jack lifts heavy loads by turning handle force into a twisting moment. Its upward motion depends on overcoming static friction between the screw threads and the jack. To study this motion, the thread can be treated as if it were a block on the groove of the jack after the thread is completely unraveled.

A free-body diagram helps show the forces acting on this simplified system. The force at the handle creates a horizontal force that pushes the movable thread up the fixed incline of the jack thread. At the same time, the load acts downward as an axial force on the thread.

The groove of the jack also pushes back on the screw thread with a reaction force. That reaction force has both normal and frictional parts, and they are linked by the coefficient of friction. The angle of static friction for impending motion is found by taking the inverse tangent of the coefficient of friction.

With these force relationships, equilibrium equations can be written for the horizontal and vertical directions. These equations describe how the applied force, the reaction forces, and the motion of the screw jack are connected. Rearranging the equations in terms of the reaction force and setting them equal leads to the moment equilibrium equation for upward impending motion.

Solving that moment equilibrium equation gives the minimum force needed at the handle to start the screw jack moving upward. This result is useful for understanding how the jack is designed and operated. It also helps the jack lift heavy loads or apply large forces when needed.

Screw Jack Force and Friction Analysis

dry friction

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upward impending motion

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key terms and concepts

Explore how a square-threaded screw jack uses force, friction, and equilibrium equations to lift loads and find the minimum handle force needed.

Screw Jack Force and Friction Analysis | 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

Screw Jack Force and Friction Analysis

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