Propulsion
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Propulsion is the generation of force by any combination of pushing or pulling to modify the translational motion of an object, which is typically a rigid body (or an articulated rigid body) but may also concern a fluid.[1] The term is derived from two Latin words: pro, meaning before or forward; and pellere, meaning to drive.[2] A propulsion system consists of a source of mechanical power, and a propulsor (means of converting this power into propulsive force).
Plucking a guitar string to induce a vibratory translation is technically a form of propulsion of the guitar string; this is not commonly depicted in this vocabulary, even though human muscles are considered to propel the fingertips. The motion of an object moving through a gravitational field is affected by the field, and within some frames of reference physicists speak of the gravitational field generating a force upon the object, but for deep theoretic reasons, physicists now consider the curved path of an object moving freely through space-time as shaped by gravity as a natural movement of the object, unaffected by a propulsive force (in this view, the falling apple is considered to be unpropelled, while the observer of the apple standing on the ground is considered to be propelled by the reactive force of the Earth's surface).
Small objects, such as
.Influencing rotational motion is also technically a form of propulsion, but in speech, an automotive mechanic might prefer to describe the hot gasses in an engine cylinder as propelling the piston (translational motion), which drives the crankshaft (rotational motion), the crankshaft then drives the wheels (rotational motion), and the wheels propel the car forward (translational motion). In common speech, propulsion is associated with spatial displacement more strongly than locally contained forms of motion, such as rotation or vibration. As another example, internal stresses in a
Vehicular propulsion
Air propulsion
An aircraft propulsion system generally consists of an
An aircraft propulsion system must achieve two things. First, the thrust from the propulsion system must balance the drag of the airplane when the airplane is cruising. And second, the thrust from the propulsion system must exceed the drag of the airplane for the airplane to accelerate. The greater the difference between the thrust and the drag, called the excess thrust, the faster the airplane will accelerate.[2]
Some
Some aircraft, like
Ground
Ground propulsion is any mechanism for propelling solid bodies along the ground, usually for the purposes of
Maglev
Maglev (derived from magnetic levitation) is a system of transportation that uses
Marine
Marine propulsion is the mechanism or system used to generate
Space
Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. There are many different methods. Each method has drawbacks and advantages, and spacecraft propulsion is an active area of research. However, most spacecraft today are propelled by forcing a gas from the back/rear of the vehicle at very high speed through a supersonic de Laval nozzle. This sort of engine is called a rocket engine.
All current spacecraft use chemical rockets (
Cable
A cable car is any of a variety of transportation systems relying on cables to pull vehicles along or lower them at a steady rate. The terminology also refers to the vehicles on these systems. The cable car vehicles are motor-less and engine-less and they are pulled by a cable that is rotated by a motor off-board.
Animal
Animal locomotion, which is the act of self-propulsion by an animal, has many manifestations, including
Locomotion requires
See also
- Jetpack
- Transport
References
- ISBN 0-85045-163-9.
- ^ a b c d "Beginner's Guide to Propulsion NASA".
- ^ "Energy Efficient - All Electric Ship". Archived from the original on 2009-05-17. Retrieved 2009-11-25.
- ISBN 978-0-19-850022-3.
External links
- Media related to Propulsion at Wikimedia Commons
- Pickering, Steve (2009). "Propulsion Efficiency". Sixty Symbols. Brady Haran from the University of Nottingham.