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.