Scale model

A scale model is a physical replica that maintains the same geometric proportions as its full-size counterpart, called the prototype. While these models are typically smaller than large prototypes like vehicles, buildings, or people, they can also be larger than tiny prototypes such as anatomical structures or subatomic particles. Scale models serve various purposes: they are used in engineering design and testing, sales and promotion, special effects for films, military planning, and hobbies like rail transport modeling, wargaming, and racing, as well as being made as toys.

Models are built to a specific scale, expressed as a ratio (e.g., 1:8) or fraction (1/8), meaning one unit on the model equals eight units on the prototype. In English-speaking countries, scale is sometimes given as inches to feet, such as 1:48 being "1 inch to 4 feet." They are constructed from plastic, wood, or metal and painted with enamel, lacquer, or acrylics. Prototypes for models include all types of vehicles (trains, cars, trucks, military vehicles, aircraft, spacecraft), buildings, people, and science fiction subjects like spaceships and robots.

Models are obtained in three ways: assembling a kit, scratch building, or collecting pre-assembled models. Scratch building, the only option for structural engineers, demands the highest skill, craftsmanship, and time, and scratch builders often prioritize accuracy and detail. Kit assembly can be done "out of the box" or with modifications called "kitbashing." Since many kit manufacturers may lack perfect accuracy, hobbyists can improve kits by adding after-market conversion kits, alternative decals, or some scratch building, without needing the master craftsmanship of a full scratch build.

Scale models generally fall into two types: static and animated. Hobbyist models are mostly built for static display, but some have operational features, like rolling trains or flying airplanes and rockets. Flying models can be simple unpowered gliders or sophisticated radio-controlled aircraft powered by miniature methanol or nitromethane engines. In slot car racing, cars in 1:24, 1:32, or HO scale use externally powered electric motors on plastic track with metal rails in slots, sometimes enhanced with miniature buildings, trees, and people. Wood car racing, such as the Boy Scouts of America's Pinewood Derby (first held in 1953), involves children carving gravity-powered cars from pine, with plastic wheels on metal axles, running on inclined tracks. Entrants receive a kit with a wooden block, four plastic wheels, and four axle nails, or may buy a commercial kit; regulations typically limit weight to 5 ounces, width to 2.75 inches, and length to 7 inches, and allow tungsten carbide weights and graphite lubricant. Miniature wargaming uses soldiers, artillery, vehicles, and scenery built by players.

Before computer-generated imagery, film and television special effects relied on miniature models—often larger in scale than hobby versions—to include fine surface detail and electrical features like interior lighting and animation. For *Star Trek: The Original Series*, a 33-inch pre-production model of the Starship Enterprise was built in December 1964 from pine, Plexiglass, and brass for $600, followed by a 135.5-inch production model made from plaster, sheet metal, and wood at ten times the cost. Given the Enterprise's fictional length of 947 feet, these models were at 1:344 and 1:83.9 scale, respectively. Polar Lights later sold a large plastic Enterprise kit at 1:350 scale (32 inches long), optionally with electronic lighting and rotating engine domes.

In structural engineering, scale models are used when problems are too complex for analytical methods or numerical techniques lack real-world confirmation—for example, a reinforced concrete beam-column-slab interaction. These models must follow the theory of similitude, scaling loading, geometry, and material properties. Structural labs, like the Newmark Civil Engineering Laboratory at the University of Illinois, test such models.