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

A wedge is a machine that is useful for adjusting the elevation of structural or mechanical parts, providing stability for heavy objects, and splitting a body into two parts.
Consider using a wedge to lift a heavy slab.
The wedge amplifies the applied force into much larger force directed almost perpendicular to the applied force.
There are seven unknowns, including the applied force for the motion of the wedge and six normal and frictional forces.
They can be determined using four force equilibrium equations applied to the wedge and the slab and three frictional equations applied at each contact surface.
To lower the slab, the frictional forces act in the opposite sense.
Provided the coefficient of friction is very small or the wedge angle is large, the applied force must act to the right to hold the slab.
If the applied force is removed and friction forces hold the block, the wedge is considered self-locking. This condition is valid only when the wedge angle is less than twice the angle made by the reaction forces.

wedges

A wedge is a simple machine that serves various purposes, such as adjusting the elevation of structural or mechanical parts, providing stability for heavy objects, and splitting a body into two parts. This versatile tool can amplify an applied force, making it easier to manipulate large or heavy objects.
Consider using a wedge to lift a heavy slab. Here, the wedge functions by converting the applied force into a much larger force directed almost perpendicular to the initial force. This amplification enables the lifting of heavy objects with minimal effort.
There are seven unknown factors involved in the motion of the wedge: the applied force and six normal and frictional forces. In the free-body diagrams, the weight of the wedge is often neglected,  as it is small compared to the load.
<img alt="Static equilibrium diagram; forces and angles in mechanics, with applied forces F1, F2, F3, and normal forces N1, N2, N3." src="/files/ftp_upload/14317/14317_PT_Figure_1v2.svg" style="text-align: center; height: 300px;" data-altupdatedat="1754904545000" data-alt="Static equilibrium diagrams, inclined plane and block, with forces F, N, angle α, and weight mg.">
These unknowns can be determined using four force equilibrium equations applied to the wedge and the slab,
<img alt="Static equilibrium equation ΣFx=0; formula for resolving forces in equilibrium analysis." src="/files/ftp_upload/14317/14317_PT_Equation_1v2.svg" style="text-align: center; height: 13px;" data-altupdatedat="1754904545000" data-alt="Static equilibrium equation: -N₃ + N₂sinα + F₂cosα = 0; physics problem-solving concept.">
<img alt="Static equilibrium equation: -F3 + N2cosα - F2sinα = mg; vector force balance diagram." src="/files/ftp_upload/14317/14317_PT_Equation_2v2.svg" style="text-align: center; height: 13px;" data-altupdatedat="1754904545000" data-alt="Static equilibrium equation, ΣFy=0; force balance, physics formula, vector components.">
<img alt="Static equilibrium equation diagram; N₁−N₂cosα+F₂sinα=0; force balance analysis." src="/files/ftp_upload/14317/14317_PT_Equation_3v2.svg" style="text-align: center; height: 13px;" data-altupdatedat="1754904545000" data-alt="Static equilibrium equation, N1-N2cosα+F2sinα=0, illustrating force balance concepts.">
<img alt="Static equilibrium; equation: F_applied - F_1 - N_2sinα - F_2cosα = 0; physics formula analysis" src="/files/ftp_upload/14317/14317_PT_Equation_4v2.svg" style="text-align: center; height: 13px;" data-altupdatedat="1754904545000" data-alt="Static equilibrium equation diagram; force balance: F applied - F1 - N2 sin α - F2 cos α = 0.">
and the remaining three frictional equations (F1, F2, F3) applied at each contact surface are given by the product coefficient of friction and their respective normal forces.
By solving these equations, one can gain insight into the relationship between the applied force and the resulting motion of the wedge.
When lowering the slab, the frictional forces act in the opposite sense. Provided that the coefficient of friction is very small or the wedge angle is large, the applied force must act to the right to hold the slab in place. This balance of forces ensures that the wedge remains stable and maintains its position while supporting the weight of the slab.
Under certain conditions, the wedge may be considered self-locking. This occurs when the applied force is removed, and friction forces alone can hold the block in place. The self-locking condition is valid only when the wedge angle is less than twice the angle made by the reaction forces.
In this case, the wedge's geometry and the friction between the contact surfaces work together to prevent unwanted movement or slippage.
The self-locking property of a wedge can be advantageous in various applications, as it provides added stability and security when manipulating heavy objects. For instance, in construction or engineering projects, a self-locking wedge can help ensure that structural components remain firmly in place during assembly or adjustments.

Wedges

A wedge is a simple machine that serves various purposes, such as adjusting the elevation of structural or mechanical parts, providing stability for heavy ...

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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

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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...

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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.

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Wedges and Self-Locking Stability

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