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1) If I place an object on a table, it will sit there forever. There's no change in potential or kinetic energy.

If I hold the object at the end of my outstretched arm, eventually I can't do it anymore. But the object is still not changing kinetic/potential energy.

Where is the loss coming from?

2) Related question: An airplane is flying level in the air. How much power is needed to keep it level?

It seems clear that any explanation will revolve around inefficiency in the force-providing mechanism, something to do with how your muscles work for the first question and something to do with drag in the airplane example.

Qmechanic
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Carlos
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1 Answers1

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Concerning the air plane:

to stay at its current altitude, the plane needs to produce enough lift to cancel gravitation. Lift is produced by moving its wings forward which then push down air. To hold its velocity, the plane must compensate for frictional forces on the plane/air.

So the energy required for holding altitude is also the energy required for holding velocity.

M.Herzkamp
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