Thought experiment on potential energy

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Discussion Overview

The discussion revolves around the concept of potential energy and its implications on mass and weight, particularly in the context of lifting objects and the effects of energy transfer within systems. Participants explore theoretical scenarios, including the mass of objects when lifted, the relationship between potential energy and inertia, and the specific case of a mousetrap in different states.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants question whether lifting an object increases its mass due to the potential energy imparted to it.
  • Others argue that potential energy is a property of the system (object + Earth) rather than the object itself.
  • A participant suggests that lifting an object causes the lifter to lose mass equivalent to the energy transferred to the object + Earth system.
  • There is a discussion about whether the mass of the object increases as it falls, with some asserting that total energy remains constant while kinetic energy increases and potential energy decreases.
  • One participant raises a follow-up question about whether the mass of an object changes from the perspective of a person who elevates themselves along with the object.
  • Several participants explore the implications of mass-energy equivalence in various scenarios, such as heating an object or stretching a spring, questioning when mass changes occur.
  • There is a debate about whether a mousetrap in the 'set' position weighs more than one that is not set, with differing opinions on how potential energy affects weight and inertia.
  • Some participants emphasize the importance of considering the entire system rather than focusing on individual components when discussing mass and energy.

Areas of Agreement / Disagreement

Participants express differing views on whether lifting an object affects its mass and whether potential energy influences weight. There is no consensus on the implications of potential energy on mass or the specific case of the mousetrap.

Contextual Notes

Participants note that the differences in perspective may stem from varying interpretations of mass and energy within classical and relativistic frameworks. The discussion highlights the complexity of defining mass in relation to energy transfer and system interactions.

  • #31
By "potential energies of all the particles", are you including gravitational potential energy?
 
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  • #32
snoopies622 said:
By "potential energies of all the particles", are you including gravitational potential energy?
That's a good question. I'd guess it would contribute to the "inertial mass" of a bound system in the usual way for an asymptotically flat spacetime (where all the mass is in the bound system, so as you get far from the mass spacetime gets arbitrarily close to the flat spacetime of special relativity), and if you look at pervect's comment #13 and pmb_phy's comment #14 on this thread, they seem to confirm this. But as pervect's link points out, talking about gravitational energy in more general circumstances (not confined to asymptotically flat spacetime) can be tricky.
 
  • #33
Thanks, JesseM; that's quite a thread. It looks like there's more to this than I thought. Maybe after another year of studying GR (I haven't learned killing vectors yet) I'll finally understand the answer to my question.

Thanks to everyone who participated in this thread!
 
  • #34
snoopies622 said:
Read the first eight entries of this thread.

Still doesn't make it any clearer. :-p

But Jesse's post appears to answer your question anyway. I was just wondering exactly what you meant, because it seemed there were a few things flying around, that might confuse the issue.
 
Last edited:
  • #35
Well, I guess the questions were: does energy always have a mass-like manifestation, and if so, where is it in the case of gravitational potential energy? I thought it might be in the mass of the objects experiencing gravitational "pull", but entry #8 suggested that it was in the field itself, which I didn't understand, since I don't know how such mass/inertia could be perceived or measured.
 

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