![]() This takes into account the factors involved in overcoming Newton's First Law.When a body is acted upon by a constant force, its resulting acceleration is inversely proportional to the mass of the body and is directly proportional to the applied force.For a constant mass, force equals mass times acceleration" Newton's second law: "Force is equal to the change in momentum per change in time.These forces may add to its motion, slow it down, or change its direction.Once it is moving, its inertia keeps it moving, subject to the various other forces acting on it.An aircraft at rest on the ramp remains at rest unless a force strong enough to overcome its inertia is applied.This means that nothing starts or stops moving until some outside force causes it to do so.A body at rest tends to remain at rest, and a body in motion tends to remain moving at the same speed and in the same direction.Newton's first law: "Every object persists in its state of rest or uniform motion in a straight line unless compelled to change that state by forces impressed on it".Note: We say lift is created by air moving faster over the top of the wing, but more specifically, its the decreased pressure which causes lift.Note: with regards to rotary-wing aircraft, lift and thrust are both in the vertical direction.As pressure above the wing decreases, the relative pressure below it is higher, creating a pressure differential which we know as lift.The rounded upper surface increases the velocity of the air, which causes pressure to decrease.Relating this principle to an airfoil, we see a similar shape.The formula shows that as the velocity of fluid (air) increases, its pressure must decrease.Assuming area is constant, you get: V 1P 1 = V 2P 2.A = Area, V = Velocity, and P = Pressure.A Venturi demonstrates Bernoulli's principle: A 1V 1P 1 = A 2V 2P 2.Bernoulli's principle demonstrates that as the velocity of a moving fluid (liquid or gas) increases, the pressure within the fluid decreases.Creation of lift can be understood by observing Bernoulli's principle as well as Newton's Laws of Motion:.This means that when performing a loop, for example, the lift vector is still perpendicular to the relative wind, which would have the lift vector pointing toward the ground as the aircraft becomes inverted.It is important to note that lift has no reference to Earth.In straight and level flight, to be effective, the total lift must overcome the total weight of the aircraft, comprised of the actual weight and the tail-down force used to control the aircraft's pitch attitude. ![]() Note that the center of lift is almost always behind the center of gravity, resulting in a nose down attitude if not countered by the tail.Lift concentrates from the Center of Lift/Pressure.This means "up" is relative to the aircraft, and being in a turn or even upside down changes the direction the lift vector points (a key principle in understanding turn performance and aerobatics).Most see a lift vector as acting "up," but instead, it acts perpendicular to the relative wind and the lateral axis of the aircraft.Common airfoils include not just the wings but the flaps/slats, and stabilizers too.The dynamic effect of the air moving across an airfoil produces lift.Lift is the critical aerodynamic force that brings an aircraft to fly.Instrument Flying Handbook, Angle of Attack and Relative Wind.
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