Does a Plane Weigh More with a Bird Inside?

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Discussion Overview

The discussion revolves around the question of whether a plane weighs more when a bird is inside it, particularly when the bird is flying. Participants explore the implications of the bird's movement on the overall weight of the plane, considering various scenarios and analogies, including the behavior of people inside the plane.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants argue that the plane does weigh more when the bird is inside because the bird exerts a downward force equal to its weight while flying.
  • Others suggest that the bird's movement does not impact the plane's weight, stating that whether the bird is flying or sitting does not change the overall weight of the plane.
  • A participant introduces a scenario involving people lifting their legs inside the plane, suggesting that if they were to lift off the floor, there would be a temporary reduction in weight, paralleling the bird's situation.
  • Another participant clarifies the difference between "lifting" and "jumping," indicating that lifting does not exert a force on the plane, while jumping does, thus affecting the weight differently.
  • There is a discussion about the implications of freefalling and the conditions under which the bird or people may not exert downward force.

Areas of Agreement / Disagreement

Participants express differing views on the impact of the bird's flight on the plane's weight, with no consensus reached. Some agree with the notion that weight changes occur under specific conditions, while others maintain that the overall weight remains constant regardless of the bird's activity.

Contextual Notes

Participants reference Newton's laws to support their arguments, but the discussion remains nuanced with various assumptions about force application and the conditions of flight and freefall.

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If a plane is flying along and inside the plane there is a little bird flapping away flying from front to back in the plane. Does the plane weigh anymore because the bird is inside it :confused: ?
 
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Yes. When the bird is flying it is exerting a downward force at least equal to its weight.
 
Ie, whether the bird is just sitting there or flying has no impact whatsoever on the flight of the plane.
 
However, when the bird is moving it's wings 'up', if we assume that for at least an instant it is not pushing air downward, and it is freefalling you might say that for that instant it did not add weight to the plane.
 
I agree with everyone, but I also agree with Decker. For example, if a jumbo-jet laden with 300 standing people(150 pounds average weight each) suddenly lifted their legs off the floor, a sudden weight reduction of 45,000 lbs. would occur. Of course, when they hit the floor, an increase would be in effect.
With respect to the bird scenario, weight cycling variations would be minimal and trivial, but would nonetheless occur given Decker's free-falling addition.
Lesson to be learned: Be certain the bird has a seat belt and it's tray is in an upright and locked position. :)
 
pallidin said:
I agree with everyone, but I also agree with Decker. For example, if a jumbo-jet laden with 300 standing people(150 pounds average weight each) suddenly lifted their legs off the floor, a sudden weight reduction of 45,000 lbs. would occur. Of course, when they hit the floor, an increase would be in effect.
Except that for a 150 lbs person to jump, he has to exert a force on the floor of the plane, thereby "adding" to its weight. See:
https://www.physicsforums.com/showthread.php?t=16844
 
If the people suddenly lift (not jump) then a force would not be exerted, but the force with which they lift must be greater than the pull of gravity
 
quantum mechanic said:
If the people suddenly lift (not jump) then a force would not be exerted, but the force with which they lift must be greater than the pull of gravity
What is the difference between "lift" and "jump"?
 
Chen said:
What is the difference between "lift" and "jump"?

A jump implies the application of a force to the ground or in this case the plane other than the force due to gravity.

Newton's 3rd law explains why a person is able to leave the floor by jumping: The interaction of the pushing of the leg against the floor of the plane.

A lift implies keeping the body stationary and simply, yet awkwardly, simultaneously making both legs not make contact with the plane. This also follows Newton's 3rd law of a force equal in magnitude oppositely directed; however, the upper body, not the plane is what pushes back. No force is initially applied to the plane other than the force due to gravity and the body begins to freefall, and as Decker stated, "if we assume that for at least an instant it is not pushing air downward, and it is freefalling you might say that for that instant it did not add weight to the plane."
 
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