Mechanisms and Their Animations

A mechanism is an assembly of connected parts arranged to transmit and transform motion in a controlled way. Mechanical engineering relies on a relatively small set of fundamental mechanisms that, combined, produce the enormous variety of motion seen in machines. Animations are particularly suited to this subject because a mechanism is defined by how its parts move relative to one another, something that a still drawing can only suggest but a moving model makes immediately clear.

Linkages are bars joined at pivots so that moving one part forces the others to follow a definite path; the four-bar linkage and the slider-crank are classic examples, the latter converting rotation into straight-line reciprocating motion. Cams and followers translate the rotation of a shaped profile into a precisely timed up-and-down or in-and-out movement, used to operate valves and to sequence operations in machinery. Each mechanism has a characteristic relationship between its input and output motion.

Gears transmit rotation between shafts while changing speed and torque according to the ratio of their tooth counts, and specialised forms such as worm gears provide large reductions in a compact space. The traditional simple machines — the lever, wheel and axle, pulley, inclined plane, wedge and screw — multiply force or change its direction and underlie these more elaborate devices. Studying how these elements move and combine builds the foundation for analysing and designing complete mechanical systems.

Frequently asked questions

What is a mechanism?

It is an assembly of connected parts arranged to transmit and transform motion in a controlled and predictable way.

What does a slider-crank mechanism do?

It converts rotary motion into straight-line reciprocating motion, or the reverse, as in the link between a crankshaft and a piston.

How do gears change speed and torque?

Meshing gears with different numbers of teeth trade speed for torque according to their ratio, so a smaller gear driving a larger one reduces speed and increases torque.