I Why does a helicopter float motionless but still consume gas?

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When a helicopter float motionless the work done on it is zero.But why does it still consume energy?A similar question is why when we hold still a weight, we must consume energy(we feel fatigue)?
 

phinds

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It is not true that no work is being done. The rotor blades do a LOT of work pushing air down and thus causing the helicopter to accelerate upwards at 9.80665 m/sec/sec in a gravitational field that is causing it to accelerate downwards at the same rate. So ... helicopter stays motionless, air moves. From the frame of reference of the air, the helicopter is moving quite a bit and is doing a lot of work.

I think the aerodynamics of it all may be a bit more complicated than that simple explanation, but you get the idea ...

The exact same question was asked recently in the form of "if I push a box across the floor against friction, I am doing work, but in MY frame of reference the box isn't moving so I'm actually NOT doing any work. What gives?" In his frame of reference he is doing work moving the floor under him. In both his question and yours, you can't get rid of the work being done just by changing frames of reference.
 

A.T.

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When a helicopter float motionless the work done on it is zero.But why does it still consume energy?A similar question is why when we hold still a weight, we must consume energy(we feel fatigue)?
Both are inefficient ways to generate a static force. The energy goes into moving air and heat.
 

berkeman

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russ_watters

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I think the aerodynamics of it all may be a bit more complicated than that simple explanation, but you get the idea ...
Due to the nature of the question, the aerodynamics are unimportant and the Newton's 3rd law + definition of work (power) explanation is all that is needed.

If I had a quibble it would be on the need to discuss reference frames here. To me it's about the proper definition of the system being analyzed. A helicopter is not a book sitting on a table, it's a fan sitting on a table. The fan does work because it's a fan!
 

Vanadium 50

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Why does a helicopter float motionless but still consume gas?
If you turned the engine off, would it continue to float?
If not, why not? (Please write a sentence for that and not a one-word answer)
 

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