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Calculations of Velocity in Propulsion

Propulsion means, literally, to push forward or to drive an object forward. A propulsion system is deisgned to propel an object forward. Northwestern University states that "Propulsion moves things like spacecraft or jet planes forward by pushing something out of the back." NASA indicates the inter-connections involved with velocity, prepulsion, Newton's (three) laws of motion, thrust and aircraft design and function.

Calculation of Velocity
- Accelerated velocity and propulsion are necessary for a jet to break gravity.
  
  To understand calculations of velocity in propulsion, we need first to understand simple calculations of velocity. Speed is equal to distance divided by time. If you travel 100 miles in two hours, your speed is two miles-per-hour. If you travel 100 miles from New York towards Florida in two hours, your velocity is 50 miles-per-hour south, since velocity, by its most accurate definition, involves direction as well as speed. Propulsion involves changes in velocity and acceleration.
Newton's Second Law as Related to Velocity and Propulsion
- Propulsion is an important factor in the design of high-velocity small aircraft.
  
  The velocity of a propelled javelin is directly related to the force with which the athlete throws it. The javelin is propelled from a stationary position, and while the athlete is running, travels along at the same velocity. However, at the moment of propulsion, the javelin accelerates at a rate faster than that of the athlete and the velocity increases. This concept is codified by Newton's Second Law of Motion, which applies to objects in which all existing forces are not balanced. The second law states that the acceleration of an object, the increase of velocity, is dependent upon the net force acting upon the object as well as the mass of the object. Larger objects require more force to propel them forward.
Force, Thrust and the Propulsion of Airplanes
- For a cargo plane, thrust and propulsion are not as important as efficiency.
  
  The propulsion of jet airplanes involves the application of Newton's third law of action and reaction (for every action, or force, in nature, there is an equal and opposite reaction). The action of some gas (or working fluid), accelerated by an engine, creates a backwards force. This propels the plane forward (the opposite reaction). The force of the propulsion of an object is indicated by the physics term "thrust," which is a mechanical force that results in a change of velocity, acceleration and momentum. The force of thrust is the change in momentum of an object with a change in time. Momentum is the object's mass times the velocity. The formula for the force known as Thrust is - F = ((m * V)2 - (m * V)1) / (t2 - t1). Thrust is the force that results in propulsion.
  
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Thrust, Mass and Moving Liquids
- When calculating thrust, the mass of the object is basically constant, and the object retains its shape when the object is in a state of propulsion. When calculating the thrust of a moving liquid, the mass is more difficult to quantify. Mass flow rate must be considered.
  
  Mass flow rate is equal to the amount of (liquid) mass moving through a given plane (surface area) over time. This is the equivalent of the density (r) times the velocity (V) times the area (A). The formula for the mass flow rate of the fluid is - m dot = r * V * A , "m dot" represents the mass flow rate, or the mass per unit time. (An additional factor that must be considered is the exit pressure (p) of the liquid if it flows at a different rate than the free steam pressure).

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