Hinges

machines · joints · movement · mechanics

Doors need hinges. A hinge is what lets a door swing open and closed. It connects the door to the frame and lets it rotate around one fixed spot, just like how a wheel spins around its center.

Your body has hinges. Your elbow and knee are actually biological hinges. They let your arm or leg bend in one direction, controlled by bones, cartilage, and muscles that work together like a mechanical hinge.

One perfect movement. An ideal hinge only lets things rotate around one axis, like a spinning wheel. It stops any sliding or sideways movement, so the two connected parts stay firmly locked together except for their rotation.

Made different ways. Hinges can be built from solid metal parts that rotate around a pin, or from flexible materials like leather or rubber. Each design works best for different jobs, from heavy steel doors to soft fabric straps.

One degree of freedom. In engineering, a hinge has exactly one degree of freedom, which means it can only move in one way. Stopping all other movements makes hinges super reliable for keeping things in exactly the right position.