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

Machines are structures made of movable, pin-connected multi-force members that form a stabilized system to transmit forces.
Consider a cutting plier used to cut a wire by applying forces on its handle.
When equal and opposite forces are applied on the handles of the cutting plier, it causes the cutting edges of the plier to come together and apply equal and opposite reaction forces on the wire, which are greater than the applied forces.
The magnitude of the forces exerted on the wire due to the applied forces can be determined by dismantling the cutting plier and drawing a free-body diagram of the components of the cutting plier.
By taking a moment about the pivot pin that holds the plier together, a relation can be established between the applied and reaction forces, which act at a distance.
Similarly, by drawing a free-body diagram for the pivot pin, the components of the internal force at the pivot pin can be determined.

machines

Machines are complex structures consisting of movable, pin-connected multi-force members that work together to transmit forces. One example of a machine is the cutting plier, which is used to cut wires by applying forces to its handles. When equal and opposite forces are exerted on the handles of the cutting plier, they cause the cutting edges to come together and apply equal and opposite reaction forces on the wire, which are greater than the applied forces.
A free-body diagram of the components of the cutting plier is considered to determine the magnitude of the forces acting on the wire due to the applied forces.
<img alt="Static equilibrium diagram with force equation, ΣFx=0, depicting pliers mechanics and leverage." src="/files/ftp_upload/14293/14293_PT_Fig_1v2.svg" style="text-align: center; height: 350px;" data-altupdatedat="1761830439000" data-alt="Figure 1">
Analyzing the moment about the pivot pin that holds the plier together can help establish a direct relationship between the applied force F and the reaction force P, with respect to their respective distances from the pivot pin.
<img alt="Power formula equation P=Fa/b; mathematical representation for physics or engineering analysis." src="/files/ftp_upload/14293/14293_PT_Equation_1v2.svg" style="text-align: center; height: 30px;" data-altupdatedat="1761830439000" data-alt="Equation 1">
Additionally, by creating a free-body diagram for the pivot pin, it is possible to determine the components of the internal force at the pivot point. Applying the horizontal force equilibrium condition, the internal force Ox is zero. Similarly, applying the vertical force equilibrium condition, the internal force Oy equals the sum of the applied force F and the reaction force P.

Machines are complex structures consisting of movable, pin-connected multi-force members that work together to transmit forces. One example of a machine ...

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KEY TERMS AND CONCEPTS

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

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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...

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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

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Cutting Pliers as a Force-Multiplying Machine

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