What Does It Mean For A Force To Act On A Particle?

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Discussion Overview

The discussion centers on the concept of what it means for a force to act on a particle, particularly in scenarios where the particle may not be in motion. Participants explore whether the mere presence of a force is sufficient to claim it is acting on a particle, or if the force must do work on the particle for this statement to hold true. The scope includes theoretical considerations and conceptual clarifications.

Discussion Character

  • Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions if a force can be said to act on a particle if the particle does not move, suggesting that the work done by the force, represented by $$\vec{F} \cdot d\vec{s}$$, may need to be non-zero.
  • Another participant argues that a force acts on a particle even if it does not move, as it can still affect the equilibrium state and energy levels of the particle and its environment, using the example of a hydrogen atom in a magnetic field.
  • A similar viewpoint is reiterated by another participant, emphasizing that the application of force changes the energy levels without necessarily causing motion.
  • A further example is provided involving a heavy body suspended by an elastic thread, illustrating that the force can be measured through the elongation of the thread, even when the body is at rest.

Areas of Agreement / Disagreement

Participants express differing views on whether a force must do work to be considered as acting on a particle. Some agree that a force can act without causing motion, while others question this perspective, indicating that the discussion remains unresolved.

Contextual Notes

Participants do not fully explore the implications of their definitions of force and work, and there are assumptions regarding the nature of equilibrium and energy states that are not explicitly stated.

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I know this is kind of a dumb question but please forgive me it's been awhile.

Is it enough for a particle to merely "feel" an external force F to state that "F is acting on the particle"?
ie if the particle was confined in a potential well and experiences F but does not move.

or does $$\vec{F} \cdot d\vec{s}$$ have to be non-zero? ie does force have to do work on the particle to state that "F is acting on the particle"?
 
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Yes, I would say that a force 'acts' on a particle even if it doesn't move. It still affects the equilibrium state, meaning that the energy level, orbit, or whatever of the particle and its surrounding environment is different when the force is applied versus when it is not applied. Force example, if you place a hydrogen atom in a magnetic field the atomic energy levels shift slightly even though the electron is still in a stationary state and isn't being ripped from its atom and accelerated away.
 
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Drakkith said:
Yes, I would say that a force 'acts' on a particle even if it doesn't move. It still affects the equilibrium state, meaning that the energy level, orbit, or whatever of the particle and its surrounding environment is different when the force is applied versus when it is not applied. Force example, if you place a hydrogen atom in a magnetic field the atomic energy levels shift slightly even though the electron is still in a stationary state and isn't being ripped from its atom and accelerated away.

Thank you!
 
Another simple example: hang a heavy body at the roof with an elastic thread; at equilibrium you can verify and measure the existence of the thread's force on the body with its elongation; cut the thread and the body falls down.

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