Do Floating Objects Have 'Weight'?

[aquaregia]

When you use a scale, you are measuring mass, and it is meaningful only if you calibrate the scale locally.

Doesn't a scale measure force?

 

[2 Big 2 Fail]

That depends on how you think of it. "Pound" is generic. Pound-force or pound-mass are more specific. I said mass, because we commonly talk about weight and weighing, and weight is mass times gravity. Of course, the ISO definition is mass times local[/] gravity, and that kind implies pound-force, if you're going to use pounds as the measure.

 

[drumkiller]

This question reminds me (if I remember correctly) of the question Charles Lindbergh asked himself while flying the Atlantic: does a (house)fly flying (as opposed to sitting) in the cockpit add weight to the aircraft? (Answer: yes.)

If the fly is flying, then it's weight can not be added to the overall weight of the plane as it is supporting it's own weight by means of lift generated from its wings. There may be some downward force generated by the fly that can cause weight fluctuations, but the static total weight will remain unchanged if the fly flys out the window.

If you have a milk jug full of water, and can convince a 1 pound weight to fly in the middle of the milk jug and not touch the sides and submerge it in water, will it weigh more or less if the flying lead weight flys out? It will weigh less, but only by the amount of water displaced by the weight, not by the weight of the weight.

 

[knowone]

I was in the back of a truck moving flooded furniture recently, travelling
at 100 kilometres per hour, and jumped in the air and became motionless.

But you don't want to do that in a small helicopter following contours.

 

[farsidefan1]

And just before the falling elevator hits the bottom wouldn't we all JUMP?

 

[Doc Harry]

F = ma

If it has mass, and there is acceleration, then it has weight.

 

[Spg01]

A plane is standing on a large treadmill or conveyor belt. The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the plane speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). Can the plane take off?

 

[RJP]

A plane is standing on a large treadmill or conveyor belt. The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the plane speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). Can the plane take off?

Faulty premise or faulty wording? If you mean that the treadmill "negates" the forward motion of the plane relative to the ground/air, then the plane is not moving, therefor there's no air rushing over it's wings. No air rushing over wings, no lift. No lift, no takeoff.

If however you mean that the plane is still moving forward along the conveyor belt then it would be possible for the plane to gain some airspeed and therefor lift.

 

[pjhansman]

The plane's source of power is the prop or jets and has nothing to do with the wheels. Therefore the conveyor speed has little impact on the plane. So the plane will get up to take-off speed, but the wheels will just be turning faster.

 

[knowone]

Too often too much speed negates the lift.