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Wikipedia writes:

Work transfers energy from one place to another, or one form to another.

Besides, physical work is always done by some force.

I cannot think up an example when some force transfers energy from one place to another (without converting energy from one form to another).

"Transfers energy from one place to another" - means energy is not changed, but just transferred (in space). I cannot imagine when work is done and there is no energy change of some kind. I thought that work is always about changing energy.

P.S. When I drag something on a rope - it is electrical energy (reaction force) to kinetic (accelerating dragged particle).

Work - is a very fundamental thing not to have a clear understanding of its deep physical essence!

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  • $\begingroup$ Why are you trying to think of an example where work is done but energy is not converted into another form? $\endgroup$
    – BioPhysicist
    Jun 14, 2018 at 14:04
  • $\begingroup$ What about a moving block colliding with another block. Kinetic energy is transfered from one to the other as work done $\endgroup$
    – Steeven
    Jun 14, 2018 at 14:06
  • $\begingroup$ @Aaron Stevens Because I think it is impossible - when work is done, energy is always (!) converted into another form. But wikipedia writes differently - my understanding differs from Wikipedia. That is why I ask - wikipedia is wrong or I am not understanding that work can be done without being converted from one form into another - wikipedia uses OR: "Work transfers energy from one place to another", OR "one form to another" - my question is about the first part before that OR. $\endgroup$
    – Code Complete
    Jun 14, 2018 at 14:09
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    $\begingroup$ I think the point of the OR is to restate the first part. Essentially wikipedia is saying the same thing two different ways. What they mean by energy being transferred from one place to another is energy being converted from one form to another. @Steeven 's comment also makes sense as well. You can't read too much into wikipedia, as the terminology used depends on who wrote the article. I wouldn't get too hung up on it. $\endgroup$
    – BioPhysicist
    Jun 14, 2018 at 14:12
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    $\begingroup$ No, in that perspective it would be kinetic -> electromagnetic -> electromagnetic -> kinetic. The electromagnetic repulsion forces push on the atoms of the other block. At collision they push them across a distance; they give them a displacement for you to use in the work-formula. $\endgroup$
    – Steeven
    Jun 14, 2018 at 20:49

1 Answer 1

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"I cannot think up an example when some force transfers energy from one place to another (without converting energy from one form to another)."

Two equal masses are joined by a string that passes over a pulley. They hang in mid air. One is given a slight upward push. It gains gravitational potential energy, while the other mass loses it. Other accompanying energy transformations (e.g. into thermal, out of kinetic) can be made as small as we like.

Will this do?

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  • $\begingroup$ The falling mass is falling (down) because of gravitation force only (now there is no counteracting upwords electromagnetic deformation/constrant/reaction force). What is happening with falling mass is that its potential energy (in gravitational field) transforms into kinetic energy. It is transformation from one form (potential energy) into another form (kinetic energy). As to the force acting to the other mass, I do not know its nature, but I am afraid it is also not an example. $\endgroup$
    – Code Complete
    Jun 14, 2018 at 14:51
  • $\begingroup$ Actually, any example to my question would a very strong counterexample which proves wrong the statement "when work is done, energy is always (!) converted into another form"... $\endgroup$
    – Code Complete
    Jun 14, 2018 at 14:51
  • $\begingroup$ About "slight upward push" - see @Steeven comment above. If there is a contact during push, it is probably electromagnetic to kinetic (accelerating upwards) and then from kinetic to potential gravitational (when decelerating and stopping at a higher altitude). $\endgroup$
    – Code Complete
    Jun 14, 2018 at 14:53
  • $\begingroup$ @Code Complete. KE can be made as small as we like by making the initial push very slight, so the motion that follows is very slow. Friction in pulley needs also to be very low. $\endgroup$
    – Philip Wood
    Jun 14, 2018 at 15:02

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