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

Un cuneo è una macchina utile per regolare l'elevazione di parti strutturali o meccaniche, fornire stabilità per oggetti pesanti e dividere un corpo in due parti.
Prendi in considerazione l'utilizzo di un cuneo per sollevare una lastra pesante.
Il cuneo amplifica la forza applicata in una forza molto più grande diretta quasi perpendicolarmente alla forza applicata.
Ci sono sette incognite, tra cui la forza applicata per il movimento del cuneo e sei forze normali e di attrito.
Possono essere determinati utilizzando quattro equazioni di equilibrio delle forze applicate allo zoccolo e alla soletta e tre equazioni di attrito applicate a ciascuna superficie di contatto.
Per abbassare la soletta, le forze di attrito agiscono in senso opposto.
A condizione che il coefficiente di attrito sia molto piccolo o che l'angolo del cuneo sia grande, la forza applicata deve agire a destra per trattenere la lastra.
Se la forza applicata viene rimossa e le forze di attrito trattengono il blocco, il cuneo è considerato autobloccante. Questa condizione è valida solo quando l'angolo del cuneo è inferiore al doppio dell'angolo formato dalle forze di reazione.

<ol>
	<li>Hibbeler, R.C. (2016). Ingegneria Meccanica: Statica. Quattordicesima edizione, New Jersey: Pearson. Pagine 430-431.</li>
	<li>Meriam, J.L., Kraige, L.G. e Bolten, J.N. (2016). Meccanica ingegneristica: statica e dinamica. Ottava edizione, Singapore: John Wiley & Sons. Pagine 353-354.</li>
	<li>Birra, F.P., Johnston, E.R., Mazurek, D.F., Cornwell, P.J. e Self, B.P. (2016). Meccanica vettoriale per ingegneri. Undicesima edizione, New York: McGraw-Hill Education. Pagine 450.</li>
</ol>

cunei

Un cuneo è una semplice macchina che serve a vari scopi, come regolare l'elevazione di parti strutturali o meccaniche, fornire stabilità per oggetti pesanti e dividere un corpo in due parti. Questo versatile strumento può amplificare una forza applicata, rendendo più facile manipolare oggetti grandi o pesanti.

Considera l'utilizzo di un cuneo per sollevare una lastra pesante. Qui, il cuneo funziona convertendo la forza applicata in una forza molto più grande diretta quasi perpendicolarmente alla forza iniziale. Questa amplificazione consente di sollevare oggetti pesanti con uno sforzo minimo.

Ci sono sette fattori sconosciuti coinvolti nel movimento del cuneo: la forza applicata e sei forze normali e di attrito. Nei diagrammi del corpo libero, il peso del cuneo viene spesso trascurato, poiché è piccolo rispetto al carico.

<img alt="Figure 1" src="/files/ftp_upload/14317/14317_PT_Figure_1v2.svg" style="text-align: center; height: 300px;" />

Queste incognite possono essere determinate utilizzando quattro equazioni di equilibrio delle forze applicate al cuneo e alla lastra,

<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;" />

E le altre tre equazioni di attrito (F1, F2, F3) applicate su ogni superficie di contatto sono date dal prodotto del coefficiente di attrito e le loro rispettive forze normali.

Risolvendo queste equazioni, si può ottenere una comprensione della relazione tra la forza applicata e il movimento risultante del cuneo.

Quando si abbassa la lastra, le forze di attrito agiscono in senso contrario. A condizione che il coefficiente di attrito sia molto piccolo o l'angolo del cuneo sia grande, la forza applicata deve agire verso destra per mantenere la lastra al suo posto. Questo equilibrio di forze garantisce che il cuneo rimanga stabile e mantenga la sua posizione mentre sostiene il peso della lastra.

In determinate condizioni, il cuneo può essere considerato auto-bloccante. Questo avviene quando la forza applicata viene rimossa e le sole forze di attrito possono mantenere il blocco al suo posto. La condizione di auto-bloccaggio è valida solo quando l'angolo del cuneo è inferiore al doppio dell'angolo formato dalle forze di reazione.

In questo caso, la geometria del cuneo e l'attrito tra le superfici di contatto lavorano insieme per prevenire movimenti indesiderati o slittamenti.

La proprietà di auto-bloccaggio di un cuneo può essere vantaggiosa in diverse applicazioni, poiché fornisce maggiore stabilità e sicurezza durante la manipolazione di oggetti pesanti. Ad esempio, in progetti di costruzione o ingegneristici, un cuneo auto-bloccante può aiutare a garantire che i componenti strutturali rimangano saldamente al loro posto durante l'assemblaggio o gli aggiustamenti.

Cunei

Un cuneo è una macchina semplice che serve a vari scopi, come la regolazione dell'elevazione di parti strutturali o meccaniche, fornendo stabilità per ...

Education

Didattica

JoVE Core

Mechanical Engineering

Ingegneria Meccanica

Unit 1

Unità 1

Friction

Attrito

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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

Static Friction at the Point of Slip

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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

Dry friction problems often focus on crates, ladders, and frames that are close to slipping. Dry friction is the force that resists relative motion, or the tendency for motion, between two surfaces in contact. In many physics and engineering problems, this force helps keep an object still or defines the point where motion is about to begin. One common case has no clear impending motion. A force may be applied to a crate, but the crate stays at rest. The friction force between the floor and the...

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

Square-Thread Screw Mechanics and Friction

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upward impending motion

Screw Jack Force and Friction Analysis

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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

Friction Torque in 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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