Name: wedges and self-locking stability
Uploaded: 2025-05-22T09:06:04.000Z
Duration: 1 min 24 s
Channel: JoVE

Une cale est une machine utile pour ajuster l’élévation de pièces structurelles ou mécaniques, assurer la stabilité d’objets lourds et diviser un corps en deux parties.
Envisagez d’utiliser une cale pour soulever une dalle lourde.
Le coin amplifie la force appliquée en une force beaucoup plus grande, dirigée presque perpendiculairement à la force appliquée.
Il y a sept inconnues, y compris la force appliquée pour le mouvement du coin et six forces normales et de frottement.
Ils peuvent être déterminés à l’aide de quatre équations d’équilibre des forces appliquées au coin et à la dalle et de trois équations de frottement appliquées à chaque surface de contact.
Pour abaisser la dalle, les forces de frottement agissent dans le sens inverse.
À condition que le coefficient de frottement soit très faible ou que l’angle du coin soit grand, la force appliquée doit agir vers la droite pour maintenir la dalle.
Si la force appliquée est supprimée et que les forces de frottement maintiennent le bloc, le coin est considéré comme autobloquant. Cette condition n’est valable que lorsque l’angle du coin est inférieur à deux fois l’angle formé par les forces de réaction.

<ol>
	<li>Hibbeler, R.C. (2016). Mécanique du génie : Statique. Quatorzième édition, New Jersey : Pearson. P. 430 et 431.</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. Pages 353 et 354.</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. 450.</li>
</ol>

les coins

Un coin est une machine simple qui sert à diverses fins, telles que l’ajustement de l’élévation de pièces structurelles ou mécaniques, la stabilité des objets lourds et la division d’un corps en deux parties. Cet outil polyvalent peut amplifier une force appliquée, facilitant ainsi la manipulation d’objets volumineux ou lourds. Considérez l’utilisation d’un coin pour soulever une dalle lourde. Ici, le coin fonctionne en convertissant la force appliquée en une force beaucoup plus grande, dirigée presque perpendiculairement à la force initiale. Cette amplification permet de soulever des objets lourds avec un effort minimal. Il y a sept facteurs inconnus impliqués dans le mouvement du coin : la force appliquée et six forces normales et frictionnelles. Dans les diagrammes des forces libres, le poids du coin est souvent négligé, car il est faible par rapport à la charge. <img alt="Figure 1" src="/files/ftp_upload/14317/14317_PT_Figure_1v2.svg" style="text-align: center; height: 300px;"> Ces inconnues peuvent être déterminées à l’aide de quatre équations d’équilibre des forces appliquées au coin et à la dalle, <img alt="Equation 1" src="/files/ftp_upload/14317/14317_PT_Equation_1v2.svg" style="text-align: center; height: 13px;"> <img alt="Equation 2" src="/files/ftp_upload/14317/14317_PT_Equation_2v2.svg" style="text-align: center; height: 13px;"> <img alt="Equation 3" src="/files/ftp_upload/14317/14317_PT_Equation_3v2.svg" style="text-align: center; height: 13px;"> <img alt="Equation 4" src="/files/ftp_upload/14317/14317_PT_Equation_4v2.svg" style="text-align: center; height: 13px;"> et les trois équations de frottement restantes (F1, F2, F3) appliquées à chaque surface de contact sont données par le coefficient de frottement et leurs forces normales respectives. En résolvant ces équations, on peut comprendre la relation entre la force appliquée et le mouvement résultant du coin. Lors de la descente de la dalle, les forces de frottement agissent dans le sens opposé. À condition que le coefficient de frottement soit très faible ou que l’angle du coin soit grand, la force appliquée doit s’appliquer vers la droite pour maintenir la dalle en place. Cet équilibre des forces garantit que le coin reste stable et maintient sa position tout en supportant le poids de la dalle. Dans certaines conditions, le coin peut être considéré comme auto–verrouillant. Cela se produit lorsque la force appliquée est retirée et que seules les forces de frottement peuvent maintenir le bloc en place. La condition d’auto–verrouillage est valide uniquement lorsque l’angle du coin est inférieur à deux fois l’angle formé par les forces de réaction. Dans ce cas, la géométrie du coin et le frottement entre les surfaces de contact agissent ensemble pour empêcher tout mouvement indésirable ou glissement. La propriété auto–verrouillante d’un coin peut être avantageuse dans diverses applications, car elle offre une stabilité et une sécurité supplémentaires lors de la manipulation d’objets lourds. Par exemple, dans des projets de construction ou d’ingénierie, un coin auto–verrouillant peut aider à garantir que les composants structurels restent fermement en place lors du montage ou des ajustements.

Les coins

Une cale est une machine simple qui sert à diverses fins, telles que le réglage de l’élévation de pièces structurelles ou mécaniques, la stabilité ...

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JoVE Core

Mechanical Engineering

Génie mécanique

Unit 1

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Friction

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Wedges

wedges and self-locking stability

A wedge is a simple machine that can lift, support, and split heavy objects. It can also change the height of structural or mechanical parts. Because it amplifies force, a wedge makes it easier to move or hold large loads with less effort.

One example is lifting a heavy slab. In that case, the wedge turns the applied force into a much larger force that acts almost perpendicular to the original push. That force change helps raise the load without requiring a large input force.

To analyze wedge motion, there are seven unknowns. These include the applied force, six normal forces, and frictional forces at the contact surfaces. The wedge weight is often ignored in the free-body diagrams because it is small compared with the load.

The unknowns can be found with four force equilibrium equations for the wedge and the slab. Three friction equations, F1, F2, and F3, are then applied at each contact surface. Each friction force equals the coefficient of friction times the normal force at that surface.

The same force balance also explains what happens when the slab is lowered. In that case, the friction forces act in the opposite direction. If the coefficient of friction is very small or the wedge angle is large, the applied force must act to the right to keep the slab in place.

A wedge can also be self-locking. This means that when the applied force is removed, friction alone can hold the block in place. The self-locking condition works only when the wedge angle is less than twice the angle made by the reaction forces.

This stability is useful in many settings. In construction or engineering work, a self-locking wedge can help keep parts firmly in place during assembly or adjustment. The geometry of the wedge and the friction between surfaces work together to reduce slipping and unwanted motion.

Wedges and Self-Locking Stability

dry friction

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static friction

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kinetic friction

Sliding Friction Between Moving Surfaces

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characteristics of dry friction

Static and Kinetic Dry Friction

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types of friction problems

Dry Friction in Crate, Ladder, and Frame Problems

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friction: problem solving

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wedges

A wedge is a simple machine that can lift, support, and split heavy objects. It can also change the height of structural or mechanical parts. Because it amplifies force, a wedge makes it easier to move or hold large loads with less effort. One example is lifting a heavy slab. In that case, the wedge turns the applied force into a much larger force that acts almost perpendicular to the original push. That force change helps raise the load without requiring a large input force. To analyze wedge...

frictional forces on screws

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upward impending motion

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self-locking screw

Screw Jack Self-Locking Behavior

A square-threaded screw jack can hold a heavy load because of its self-locking behavior. This feature makes the device more reliable when it is used to lift large weights or apply a strong force. If the screw keeps its position after the turning moment is removed, the jack is self-locking. Self-locking happens because friction changes the way the forces act on the thread. The friction force reverses direction, and the reaction force moves to the other side of the thread’s normal. In this case,...

screw: problem solving

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frictional forces on flat belts

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flat belts: problem solving

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pivot bearings

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collar bearings

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journal bearings

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bearings: problem solving

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rolling resistance

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rolling resistance: problem solving

Lawn Roller Force Calculation

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key terms and concepts

Learn how wedges amplify force, lift heavy slabs, and stay in place through friction. Explore equilibrium, contact forces, and self-locking stability.

Wedges and Self-Locking Stability | 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

Wedges and Self-Locking Stability

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