Human power in the context of "U.S. Navy"

A machine is a thermodynamic system that uses power to apply forces and control movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to natural biological macromolecules, such as molecular machines. Machines can be driven by animals and people, by natural forces such as wind and water, and by chemical, thermal, or electrical power, and include a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement. They can also include computers and sensors that monitor performance and plan movement, often called mechanical systems.

Renaissance natural philosophers identified six simple machines which were the elementary devices that put a load into motion, and calculated the ratio of output force to input force, known today as mechanical advantage.

Human-powered transport is the transport of person(s) and/or goods (freight) using human muscle power. Unlike animal-powered transport, human-powered transport has existed since time immemorial in the form of walking, running and swimming, as well as small vehicles such as litters, rickshaws, wheelchairs and wheelbarrows. Modern technology has allowed mechanical advantage devices and machines to enhance human-power.

Although motorization has increased speed and load capacity, many forms of human-powered transport remain popular for reasons of cost, convenience, leisure, physical exercise and environmentalism. Human-powered transport is sometimes the only type available, especially in underdeveloped or inaccessible regions.

Human-powered land vehicles are land vehicles propelled over ground by human power, The main ways to support the weight of a human-powered land vehicle and its contents above the ground are rolling contact; sliding contact; intermittent contact; no contact at all as with anything carried; or some combination of the above. The main methods of using human power to propel a land vehicle are some kind of drivetrain; pushing laterally against the ground with a wheel, skate, or ski that simultaneously moves forward; by pushing against the ground directly with an appendage opposite to the direction of travel; or by propeller. Human-powered land vehicles can be propelled by persons riding in the vehicle or by persons walking or running and not supported by the vehicle.

Many human-powered land vehicles can also be gravity-powered land vehicles, and vice versa, although some of the latter are quite awkward to use as the former. For example: street luges, gravity racers, and snow boards.

In landscape architecture and garden design, a water feature is one or more items from a range of fountains, jeux d'eau, pools, ponds, rills, artificial waterfalls, and streams. Before the 18th century they were usually powered by gravity, though the famous Hanging Gardens of Babylon are described by Strabo as supplied by an Archimedean screw and other examples were supplied with water using hydraulic rams.

Ancient water features were powered using gravitational forces, human power or animals to pump in the water. Since the 18th century, the majority of water features have been powered by pumps. In the past, the power source was sometimes a steam engine, but in modern features it is almost always powered by electricity. There is an increasing range of innovative designs as the market becomes more established and people become more aware of alternate installation methods, such as solar power. The advantages of using solar power include environmental benefits, no electrical lines in the garden, and free energy.