Name: cutting pliers as a force-multiplying machine
Uploaded: 2023-09-22T11:49:25.000Z
Duration: 1 min 19 s
Channel: JoVE

K12 Standards

Arizona Science Standards

High School

Physical Science

HS.P3

HS.P3U2.7

Machines

Le macchine sono strutture costituite da elementi multiforza mobili e collegati a perni che formano un sistema stabilizzato per trasmettere le forze.
Considera una pinza da taglio utilizzata per tagliare un filo applicando forze sul suo manico.
Quando vengono applicate forze uguali e opposte sui manici della pinza da taglio, i taglienti della pinza si uniscono e applicano forze di reazione uguali e opposte sul filo, che sono maggiori delle forze applicate.
L'entità delle forze esercitate sul filo a causa delle forze applicate può essere determinata smontando la pinza da taglio e disegnando un diagramma a corpo libero dei componenti della pinza da taglio.
Soffermandosi un attimo sul perno di articolazione che tiene insieme la pinza, è possibile stabilire una relazione tra le forze applicate e quelle di reazione, che agiscono a distanza.
Allo stesso modo, disegnando un diagramma a corpo libero per il perno di articolazione, è possibile determinare le componenti della forza interna al perno di articolazione.

<ol>
	<li>Hibbeler, R.C. (2016). Ingegneria Meccanica \u2012 Statica e Dinamica. Hoboken, New Jersey: Pearson Prentice Hall. pagine 305</li>
	<li>Birra, F.P.; Johnston, E.R.; Mazurek, D.F; Cromwell, P.J. e Self, B.P.(2019). Meccanica vettoriale per ingegneri \u2012 Statica e dinamica. New York: McGraw-Hill. pagine 107 - 348</li>
</ol>

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macchine

Le macchine sono strutture complesse costituite da elementi mobili collegati tra loro da perni e sottoposte a forze multiple, che lavorano insieme per trasmettere forze. Un esempio di macchina è la pinza tagliante, utilizzata per tagliare fili applicando forze alle sue impugnature. Quando sulle impugnature della pinza tagliante vengono esercitate forze uguali e opposte, le lame di taglio si avvicinano e applicano al filo forze di reazione uguali e opposte, maggiori delle forze applicate.

Viene considerato un diagramma dei corpi liberi dei componenti della pinza tagliante per determinare la grandezza delle forze che agiscono sul filo a causa delle forze applicate.

<img alt="Figure 1" src="/files/ftp_upload/14293/14293_PT_Fig_1v2.svg" style="text-align: center; height: 350px;" />

Analizzando il momento intorno al perno che tiene insieme la pinza, è possibile stabilire una relazione diretta tra la forza applicata F e la forza di reazione P, rispetto alle rispettive distanze dal perno.

<img alt="Equation 1" src="/files/ftp_upload/14293/14293_PT_Equation_1v2.svg" style="text-align: center; height: 30px;" />

Inoltre, creando un diagramma dei corpi liberi per il perno di rotazione, è possibile determinare le componenti della forza interna nel punto di perno. Applicando la condizione di equilibrio delle forze orizzontali, la forza interna Ox è zero. Allo stesso modo, applicando la condizione di equilibrio delle forze verticali, la forza interna Oy è uguale alla somma della forza applicata F e della forza di reazione P.

Macchine

Le macchine sono strutture complesse costituite da elementi multiforza mobili e collegati a perni che lavorano insieme per trasmettere le forze. Un esempio di macchina ...

Education

Didattica

JoVE Core

Mechanical Engineering

Ingegneria Meccanica

Unit 1

Unità 1

Structural Analysis

Analisi Strutturale

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

cutting pliers as a force-multiplying machine

Cutting pliers are a machine that helps transmit force through movable, pin-connected members. In this example, the handles and cutting edges work together to cut wire by turning an input force into a larger output force at the jaws.

When equal and opposite forces are applied to the handles, the cutting edges move toward each other. They then apply equal and opposite reaction forces to the wire. These reaction forces are greater than the forces applied to the handles, which is why the wire can be cut.

A free-body diagram of the plier parts is used to find the size of the forces acting on the wire. Taking the moment about the pivot pin, the pin that holds the pliers together, gives a direct link between the applied force F and the reaction force P. That relationship depends on how far each force acts from the pivot pin.

A free-body diagram of the pivot pin also shows the internal force at that point. Using horizontal force equilibrium, the internal force O x is zero. Using vertical force equilibrium, the internal force O y equals the sum of the applied force F and the reaction force P.

Cutting Pliers as a Force-Multiplying Machine

cutting-pliers-as-a-force-multiplying-machine

introduction to structures

Structure Types and Force Paths

Structures are systems of interconnected members that support or transfer forces and handle the loads placed on them. Engineers can find the internal forces in a structure by breaking it apart and drawing free-body diagrams for individual members or groups of members. This helps show how structural elements behave and how the whole system stays stable under load. There are three main categories of structures: trusses, frames, and machines. Trusses are stationary structures that stay rigid when...

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Truss Joint Force Analysis by Equilibrium

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method of joints: problem solving ii

Truss Force Analysis at Joints A to E

Truss force analysis at joints A to E uses the method of joints to find the force in each member. The truss has frictionless joints, a wall support, and a roller support. A 150 N force is applied at joint A, and the member forces are solved from joint to joint. First, the angle between members AC and AB is found using the inverse tangent of the ratio of BC to AB. This gives an angle of 67.38°. A free-body diagram of joint A is then drawn, and each unknown force is split into vertical and...

zero-force member

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method of sections

Truss Member Force Analysis by Sections

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method of sections: problem solving i

Truss Member Force Calculation by Sections

Truss member forces can be found with the method of sections in a symmetrical roof truss. The structure here includes vertical, diagonal, and horizontal members. Each horizontal member is 4 m long. The vertical members FB and HD are 4 m long, and member GC is 6 m long. The roof truss carries loads at several joints. Joints F, G, and H each have a 2 kN load. Joints A and E each have a 1 kN load. To start the analysis, moment equilibrium is used at point A. The force and distance values are...

method of sections: problem solving ii

Truss member force analysis by sections finds the forces in selected members of a wall-mounted truss. The structure here includes diagonal, vertical, and horizontal members. The known loads and member lengths are used to solve for the forces in CB, GB, and GH. A cut is made through members CB, GB, and GH. The right side of the truss is then isolated as a free-body diagram. Next, the moment equilibrium equation is taken about point G. This step gives the force in member CB as 4 kN, and the...

space trusses

Space Truss Forces and Stability

A space truss is a three-dimensional truss made from members joined at their ends. It is the 3D version of a planar truss. These frameworks often use ball-and-socket joints, which help the structure stay stable and flexible under load. Space trusses are used in many construction projects because they can adapt to complex forces. Their basic building block is the tetrahedron. A tetrahedron has six members and four triangular faces. Engineers can build larger space trusses by adding one joint...

space trusses: problem solving

3D Truss Force Analysis with Joint Equilibrium

A space truss is a three-dimensional truss structure made of members connected at their ends. It often uses ball-and-socket joints to form a stable and versatile framework. Because it can handle complex loads, this type of structure is used in many construction projects. The example begins with a tripod made from a tetrahedral space truss. A ball-and-socket joint is located at C. The height and the lengths of the horizontal and vertical members are known. A tensile force is applied at joint D.

frames

Frame Analysis in Structural Systems

Frames are important parts of many mechanical and structural systems used every day. They are valued for stability and for their ability to bear heavy loads. A frame is built from two-force members and multi-force members, and the parts are connected with pin joints. Trusses are different because they are made entirely of two-force members. Frames appear in many practical settings. They can support beams and columns in buildings. They are also used in automobile chassis construction. In the...

frames: problem solving i

Jib Crane Reaction Forces in Frames

Jib crane reaction forces in frames are found by analyzing the pin joints, the cable tension, and the load carried by the pulley. The structure in this problem has an external load suspended from the pulley, and the member sizes are shown in the figure. Because the pulleys are frictionless, the force balance can be worked out step by step. The frame has two main parts. Member BD is a two-force member, which means it is a straight part loaded only at its two ends, D and B. Those end forces are...

frames: problem solving ii

Hydraulic Hoist Force Analysis

Hydraulic hoist force analysis shows how to find the forces in key members of a simple frame. The load is 1 kN, and the structure is represented with known member dimensions. In this setup, BF and BD act as two-force members. EFG and EDC are multi-force members, so each one is analyzed with a free-body diagram. The first step is to study member EFG. The inclined force in BF is split into vertical and horizontal parts. Then the moment equilibrium condition is applied at joint E. Using this...

machines

Cutting pliers are a machine that helps transmit force through movable, pin-connected members. In this example, the handles and cutting edges work together to cut wire by turning an input force into a larger output force at the jaws. When equal and opposite forces are applied to the handles, the cutting edges move toward each other. They then apply equal and opposite reaction forces to the wire. These reaction forces are greater than the forces applied to the handles, which is why the wire can...

machines: problem solving i

Toggle Clamp Force Analysis

A toggle clamp can be analyzed to find its clamping force from a known handle force. In this example, a 200 N force is applied at the handle. The clamp is used in holding and clamping tasks in woodworking, metalworking, and assembly operations. The toggle clamp is a machine structure made of movable, pin-connected multi-force members. These members form a stabilized system that transmits force. Member CD is a two-force member, which means the forces at its ends are equal in magnitude and...

machines: problem solving ii

Lifting Tong Force Analysis

Lifting tong force analysis shows how forces move through a pin-connected machine. The structure uses movable sections DAF and CBG with member AB linking them together. Because these parts work as connected members, the load can be studied with equilibrium methods. The example starts with a 100 kg load at point E. The load weight is found by multiplying mass by gravity, which gives 981 N. The cable tension acts upward and balances that weight. Since the structure is symmetrical at E, the...

key terms and concepts

See how cutting pliers act as a machine, using a pivot pin, free-body diagrams, and force balance to produce a larger cutting force on wire.

Cutting Pliers as a Force-Multiplying Machine | 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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9-12

SPS8.

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Cutting Pliers as a Force-Multiplying Machine

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