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The process of causing a body to move by exerting a force against it.


The process of causing a body to move by exerting a force against it. Propulsion is based on the reaction principle, stated qualitatively in Newton's third law, that for every action there is an equal and opposite reaction. A quantitative description of the propulsive force exerted on a body is given by Newton's second law, which states that the force applied to any body is equal to the rate of change of momentum of that body, and is exerted in the same direction as the momentum change.

In the case of a vehicle moving in a fluid medium, such as an airplane or a ship, the required change in momentum is generally produced by changing the velocity of the fluid (air or water) passing through the propulsive device or engine. In other cases, such as that of a rocket-propelled vehicle, the propulsion system must be capable of operating without the presence of a fluid medium; that is, it must be able to operate in the vacuum of space. The required momentum change is then produced by using up some of the propulsive device's own mass, which is called the propellant. See Aerodynamic force

The two terms most generally used to describe propulsion efficiency are thrust specific fuel consumption for engines using the ambient fluid (air or water), and specific impulse for engines which carry all propulsive media on board. See Specific fuel consumption, Specific impulse

The energy source for most propulsion devices is the heat generated by the combustion of exothermic chemical mixtures composed of a fuel and an oxidizer. An air-breathing chemical propulsion system generally uses a hydrocarbon such as coal, oil, gasoline, or kerosine as the fuel, and atmospheric air as the oxidizer. A non-air-breathing engine, such as a rocket, almost always utilizes propellents that also provide the energy source by their own combustion.

Where nuclear energy is the source of propulsive power, the heat developed by nuclear fission in a reactor is transferred to a working fluid, which either passes through a turbine to drive the propulsive element such as a propeller, or serves as the propellant itself. Nuclear-powered ships and submarines are accepted forms of transportation. See Turbine propulsion

References in periodicals archive ?
The stroke was defined as the instant of propulsive force increased abruptly until it reached its lowest point (Dos Santos et al.
Jet-propelled medusae reach high velocities and are thus highly proficient swimmers, but this propulsive strategy is energetically inefficient compared to other modes (Daniel, 1985; Sahin et al.
The open rotor engine can achieve potentially greater improvements in propulsive efficiency than a turbofan but lacks the containment and noise reduction benefits of a duct.
Notwithstanding the defendants' attorney's extraordinary efforts to elicit testimony from his own expert medical witness that the injuries to the child resulted from the maternal propulsive forces of labor, the defendants' expert medical witness, much to the chagrin of the defendants' counsel consistently stated that he could not give an opinion as to whether the maternal propulsive forces of labor caused the injuries to the child, or, in the alternative, whether or not the injuries to the child were the result of excessive force being used by Nurse Kuney.
But it can also be one of the hippest, swingingest, most propulsive instruments used in jazz.
Opening with the propulsive "Fairfield '72," Harris' bandmates (guitarist Musashi and flautist Jonathan Dyer) find a pocket and lock into a groove through to the closing track (the lounging "Return to Vegas") that's nostalgic yet original and in the moment.
A collage of relentless diagonal strips of red and black paper, which are slightly at odds with a canted grid of squares cut from and returned to the surface, it suggests the propulsive dynamism--and palette--of El Lissitzky's "Prouns" but might also be put to good use as a No Wave album cover.
Produced and cowritten by Stuart Price (Los Rythmes Digitales), Confessions is sequenced for nonstop movement, and the songs are propulsive enough that lyrics become irrelevant--until you pay attention to them, that is, like on the annoyingly kabbalistic "Isaac," But the winners here, such as the lead single "Hung Up," with its giddy, gimmicky ABBA loop, and the minor-key disco urgency of "Get Together," are as bright and shiny and fun as any old-school "Burning Up" moment your memory can conjure.
The inmost texture of his being is propulsive, and there is nothing more intimately bound up with his success than mobility and devotion to transcendent aims.
Two horses consistently changed from braking to propulsive forces at 22.
These would come under the headings of experimental minimalism, sequencer-driven instrumentals, film themes and a throbbing, propulsive dance style.