It takes no energy to hold anything steady.
I misunderstood. Thanks so much.
Here, hold this 100-pound sack of flour for a few hours.
If the question is “work = force x distance” when dragging a weight along the floor against friction resistance, then why is it not work when holding a weight steady against force of gravity or a plunger held steady against the force of air pressure?
Energy is a measure of ability to do work - your muscles have (chemical) energy. They expend it holding something in equilibrium against an opposing force. The plunger or bowling ball, of course, does not gain energy.
Because your muscles are moving when doing work. They are contracting, so they will tire out.
If you lie down and I place a bowling ball on your chest, you can hold it steady without doing any work.
Because the distance is zero.
As Chronos notes, the distance traveled by the item is zero; you have not done any work, i.e. you have not transferred any mechanical energy, to the object.
This is unique to the physiological mechanism of your muscles. Note that a cable suspending a bowling ball from the ceiling is not doing any work on the bowling ball, and it’s also not expending any energy to create that force. Likewise, your muscles don’t do any work on a bowling ball when they hold that ball at constant altitude - but your muscles, because of how they operate, are pissing away energy internally in order to exert that steady force.
A hovering helicopter is a related example. No mechanical work is being done on the chassis of the helicopter - but the engine and rotor are pissing away energy in order to exert the force required to offset gravity. You could take away the engine and rotor and set the chassis on top of a flagpole; from the chassis’ point of view it’s the same thing, i.e. no work is being done on it.
Because muscles are inefficient. Just because you used up energy doesn’t mean you actually did work. A helicopter hovering in one spot hasn’t done any work, but it still uses fuel because a helicopter is an inefficient method of keeping something stationary.
I’m probably just being nitpicky because physics can claim I didn’t do any work after I busted ass holding up 100lbs, but I think that helicopter is doing lots of work. I think the air it’s hurling at the ground would agree if it could.
And I predict someone will correctly nitpick my nitpick. Don’t disappoint me, folks.
ETA: And Machine Elf didn’t get nitpicked because I can’t find a nitpick with his statement.
The physics concept of work is an exercise in theoretical physics that applies to spherical chickens in a vacuum.
The concept does not really take into account the exertion of effort (to avoid the technical terms “work” or “energy”). Obviously performing an essentially isometric exercise like a person holding up a weight against gravity, or a helicopter or rocket or Harrier jet hovering, is using energy in the strict, measurable sense.
A bowling ball resting on a table (or on you lying down) converts a small amount of potential energy into deformation and compression of the supporting surface as it sinks however much to reach equilibrium. That work is “recovered” in that t is slightly easier to lift it the first fraction on a centimeter as the table rebounds (or the ball drops slightly less of a distance as it rolls off the table, and then the table top rebounds, releasing spring-like potential energy).
Similarly, your muscles convert biological energy (glucose?) into heat while maintaining a pose; the engine in the helicopter burns fuel and creates circular motion of the blades against air resistance, creates heat and motion of the air, vibrations (noise) in the air, radiant heat, etc.
Once you get into second and third level detail, the physics is a lot less theoretical…
I’ll be more precise: A helicopter carrying a 100-lb weight and hovering (i.e. stationary in the air) is not doing any work on the 100-lb weight. It’s doing work on air, any loose object being blown around by the air flow, etc.
Similarly, a person holding a 100-lb weight is not doing work on the weight, but the muscles may be generating heat, twitching, etc.
Nitpick resolved. Plus, I’m even more sorry about being butthurt about physics denigrating my “work”. 