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Newton's First and Second Laws

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The Forces of Flying
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The Forces of flying

Credit: xlibber
Source: http://www.flickr.com/photos/56844661@N00/3423766012
License: CC BY-NC 3.0

Flight is a delicate balance of the forces on the airplane. By properly shaping the aircraft, you can maximize the forces you want more of and reduce the forces you want less off.

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  • There are four main forces in flight: 
    • lift
    • drag
    • thrust
    • weight 
  • Each of these four forces has a counterpart whose vector points in the opposite direction. These pairs are lift and weight, and thrust and drag.
  • Thrust and Drag: Thrust in an aircraft is achieved through the use of the engine and some type of propeller or some type of nozzle to expel air. The thrust that is needed must be able to exceed the magnitude of drag that will the aircraft will experience when the trying to accelerate. Since the drag that is experienced is not linear with respect to the velocity of the aircraft, the greater velocity you wish to achieve, significantly larger amounts of energy must be used to combat the increasing drag forces.
  • Lift and Weight: By using Newton's 2nd law, for an airplane to move along the vertical axis, the lift needs to be greater than the weight for an aircraft to take off from the ground. Lift on an aircraft is achieved primarily through the design of the wings. As air hits the leading edge of an aircraft wing, the flow of air above the wing is faster than the flow of air underneath. Because the flow is slower under the wing, the pressure is greater. Bernoulli's principle states that this pressure is greater will try to move to a region of lower pressure, namely, up. This difference in pressure is what generates the lift upward on the wing.
  • While the full dynamics of flight can be rather complex and consist of multiple variables, the primary forces to be considered will never change.
  • Learn more about the forces on an airplane: 

https://www.khanacademy.org/partner-content/mit-k12/mit-k12-physics/v/the-forces-on-an-airplane

  • Learn more about the aerodynamics of flight:

http://www.youtube.com/watch?v=5ltjFEei3AI

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Using the information provided above, answer the following questions.

  1. The force of air resistance is usually equal to bv^2, where v is the velocity and b is a constant. What is this constant?
  2. Would lift be needed on a plane that was suddenly put in deep space?
  3. Why is there usually a minimum speed required for planes to take off?

Image Attributions

  1. [1]^ Credit: xlibber; Source: http://www.flickr.com/photos/56844661@N00/3423766012; License: CC BY-NC 3.0

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