Newton’s Laws
Although the Bernoulli
Principle is used to describe many physical phenomena, it does not explain
lift. Luckily for us there is a much
more sound explanation for how an airplane flies! There are four main forces that act on an airplane wing
during flight: lift, weight, thrust, and drag. To further explain the
physical phenomena that lift a plane during flight, I will instead use Newton’s
Laws.
A very generalized depiction of the four major forces acting on a plane during flight. (www.aviation-history.com/theory/force.gif) Let’s say a plane is flying at a constant velocity and is not changing in altitude. Newton’s first law states: “Any object at rest will remain at rest or an object in motion will remain in motion unless a force acts on it.” Newton’s second law tells us that the sum of the forces (F) acting on a body is the mass (m) times the acceleration (a) of the body. In the case of our airplane, there is no acceleration because the velocity does not change up or down, forwards or backwards, so the sum of the forces must be zero. (F = ma = 0) In the case of the up and down forces, we know that the weight of the plane is acting down, so the counteracting lift force must be of magnitude equal and opposite the weight (which can be very large depending on the size of the airplane in question)!
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