Physical Science 1 Flashcards
The four forces that act on a plane are lift, weight, drag or air resistance, and thrust, the last of which is produced by the plane’s engine.
Impact pressure produces 30% of the lift. It results from the fact that wings are given a dihedral angle where the distance from the tip of the wing to the ground is greater than that from the root of the wing to the ground.
The other 70% of lift can be accounted for by the Bernoulli effect. A cross-section of an airplane’s wing reveals greater surface area above the wing compared to a flatter, lower surface. Thus air, moving in streamline flow, must move more rapidly over the top of the wing.
Bernoulli’s equation, P + 1/2ρv2 + ρgh = constant, is often modified when discussing an airplane’s wing. The “ρgh” component is usually left out since the difference in distance from the top of the wing to the ground compared to the bottom of the wing to the ground is usually negligible.
Newton’s Third Law states that for every action there must be an equal and opposite reaction. This is applicable to lift and the dihedral angle because:
A.) the fast moving air above the wing increases the pressure.
B.) drag must be as low as possible to improve forward motion.
C.) there is a large pressure difference between the wings.
D.) the wing deflects the air downward and the air in turn deflects the wing upward.
Correct Answer: D
A. is untrue as the fast moving air causes a lower pressure in the region above the wing (see Q2). B. has no relation to the question. C. is false because such a difference in pressure between the wings would lead to serious imbalances during flight. D. is correct and is the only answer which refers to two forces acting in opposite directions on the same object.
The four forces that act on a plane are lift, weight, drag or air resistance, and thrust, the last of which is produced by the plane’s engine.
Impact pressure produces 30% of the lift. It results from the fact that wings are given a dihedral angle where the distance from the tip of the wing to the ground is greater than that from the root of the wing to the ground.
The other 70% of lift can be accounted for by the Bernoulli effect. A cross-section of an airplane’s wing reveals greater surface area above the wing compared to a flatter, lower surface. Thus air, moving in streamline flow, must move more rapidly over the top of the wing.
Bernoulli’s equation, P + 1/2ρv2 + ρgh = constant, is often modified when discussing an airplane’s wing. The “ρgh” component is usually left out since the difference in distance from the top of the wing to the ground compared to the bottom of the wing to the ground is usually negligible.
2) Compared to the wing’s upper surface, the air moving along the undersurface has:
A.) greater velocity, greater pressure.
B.) greater velocity, lower pressure.
C.) lower velocity, greater pressure.
D.) lower velocity, lower pressure.
Correct Answer: C
A. and B. are false as stated in the passage (paragraph 3, line 5). Next, let’s look at a bit of math: given “xy + z = constant,” means that if z increases, then xy must decrease for the equation to remain constant; if z remains the same but x doubles, then y must be halved for the equation to remain constant; etc. Let’s look at the equation you’re given: Bernoulli’s equation:
P + (1/2)ρv2 + ρgh = const.
We are told (P3, L5) that air (= a fluid) flows more rapidly (= greater velocity, v) above the wing than below the wing. Thus if the velocity ‘v’ is less below the wing, according to Bernoulli’s equation, the pressure ‘P’ must be higher below the wing in order to keep the equation constant. {A Phun with Physics Phact: wings are shaped as they are (P3) in order to allow pressure to increase under the wing which provides the force of ‘lift’ for the airplane and allows it to fly!}
