Work function- Valid or invalid

[Indroneil Ghosh]

The work function is a very basic concept. Some people lately have been dismissing this function very rudely.

 

The justification given is this:

If one keeps pushing something immovable, he/she gets real tired but no work is done. So questions arise:

Where does all the energy of the person go? ;)

Why does he get tired at all when no work is done?:eek:

 

Such a basic confusion. I mean if such basic questions can be framed to defeat the validity of the work function, how much of our science is going to become invalid!

 

Can anyone please answer these questions?

[Indroneil Ghosh]

Reward System... :) :eek: ;)

 

People do not want to work if it's pointless to them.

Give them something to work towards....

;)

That is defenitely not the answer I expected.

[Jay-qu]

they get tired because they are expending energy which goes into heat from their body.

[Indroneil Ghosh]

Well said.

 

But that is the amount of energy that must be released. I mean that much heat energy would also be lost if we do excersise with weights and become equally tired. Actually, more heat would be released. It is a indirect result from the second law of thermodynamics.

 

Will all the energy be lost as heat? I mean if we calculate the energy released from respiration (by using hess's law to guess how much energy would be release by total use of the glucose used up) it should be much higher than what we get.

 

This is getting confusing...;)

[Erasmus00]

The reason your muscles get tired when you push something doesn't move has to do with the way your muscles work. Your body isn't designed to "lock" your arms (or legs) into any one position, so the muscles can't expend a completely steady force. Instead, as your nerves fire, your muscles expand and contract repeatedly, which is where the energy goes.

-Will

[TheBigDog]

When two equal men are arm wrestling there appears to be no motion at all where they are gripping each other. But even if they appearing motionless they are exerting energy that is resisting the energy of the other. The same is true of a man puching on a huge boulder. The boulder never moves, but from a relativity point of view the man sees the boulder as moving toward him, and the boulder sees the man as moving toward it. The man does not have the energy to overcome the inertia (in a state of static friction) of the boulder and his motion is redirected despite his exhertion. In a frictionless environment there would be measureable motion of both objects in exchange of energy. It is the friction between bodies caused by gravity holding us to the earth that makes the illusion that you perceive as nothing happening.

 

Bill

[Lsos]

All the energy probably does get wasted as heat. Still, I doubt you're expanding nearly as much energy merely pushing on something as you are when actual work is being done. Many times at the gym I was able to hold a weight in position for a couple seconds, but try as I would I could not get it to move.

[Farsight]

We discussed this on the recent thread A problem with KE = ½mv². Help. What I came away with was this, if I might offer it as a simple concept:

 

Work and Energy are both measured in Joules, and are almost the same thing in Work is the amount of Energy transferred from one system to another. And as far as dynamics is concerned, IMHO the best word to describe Energy is "pushing". I don't mean the act of pushing, I mean an amount of pushing.

 

If you "push" a mountain for an hour it doesn't move. So you haven't really pushed it, you've pressed it. All your work is wasted, dissipated in heat and stress and sweat.

 

But if you push a car, it does move, and your work pushing it has gone into the car. It's now got "pushing". Energy. If you run round and stand in front of it you can feel how much. Note that something has to move to have "pushing". Something massive moving fast will have more of it than something small moving slow. And there's more "pushing" than just mass x velocity - you can understand the ½mv² if you remember that when you pushed the car, you had to push yourself faster and faster, and then push the car just like you did at the outset.

 

Something that isn't moving now can also have "pushing" if you can do something to it to release the motion. You can think to yourself how much "pushing" a coiled spring has got stored up within it. How much "pushing" is locked up in here, how much "energy"? The answer is in Joules. Or maybe the answer to to rename Joules to Pushings!

[Farsight]

Sorry, slip of the tongue. When I said:

 

If you "push" a mountain for an hour it doesn't move. So you haven't really pushed it, you've pressed it. All your work is wasted, dissipated in heat and stress and sweat.

 

I should have said All your effort is wasted, because you didn't do any "Work". You didn't make it move. You didn't give it any of your "pushing". And no matter how hard you press, no matter how much force you exert, you still won't.

 

There's an awful lot of confusion in the words when it comes to physics. I hope I haven't caused any more.

[arkain101]

They exert a force, so all kinds of work is going on in them at the cellular and atomic level. Everything is moving there.

 

You can extert force and not move the object of "target" and you have not "worked" it. Yet you can still expend energy cause it goes to different places.

 

The reason we dont care about the other places is because the equations arent targeted to that business at the moment.

 

The work that is important is the object getting moved. Then you have moved a force over a distance, but our bodies are not a perfect collsion interaction, we are a jiggly heat exerting life form. If we jump off a ladder and try to shove that imovable object down and cant, then we didnt do work we just fell and bounced. so to speak.

 

Yes, its weird that people mess with the work function. Its aimed at basics for a reason.

[Pyrotex]

The work function is a very basic concept. ...Where does all the energy of the person go? Why does he get tired at all when no work is done...

As often happens in Science, words that are assigned specific technical meaning also get used in common every-day speech, where they evolve and eventualy take on meanings comlpletely different from the Scientific usage.

 

In Science-speak, "work" means the integration of force over distance. It is a mathematical concept.

 

In common-speak, "work" means effort, force, push, production, accomplishment, attempt, looking busy, success (as in, the program worked), motion, turned on (as in the working motor), not broken (as in the working motor), sweat, expend energy, dig, push buttons, use a keyboard, and 1000 other variations.

 

The confusion lies with people attempting to engage in Science-speak, but they think their common-speak definitions for the word are the same. They aren't.

 

If you push against an unmoving mountain, you are NOT doing WORK(science), though you MAY be doing WORK(common). These are

 

totally different words with totally different meanings that just happen to be spelled the same. Similar problems occur with words such as Energy, Force, Power.

[Tim_Lou]

the object will get compressed very very slightly. so some of your energy goes into the potential energy of the compression. (kinda like a spring)

 

and you will do work since the displacement is the compression distance.

[arkain101]

the object will get compressed very very slightly. so some of your energy goes into the potential energy of the compression. (kinda like a spring)

 

and you will do work since the displacement is the compression distance.

 

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