Force Analysis of a compressed spring

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Discussion Overview

The discussion revolves around the forces involved when a person exerts a force to compress a horizontally placed spring against a wall. Participants explore the relationship between the forces acting on the spring and the person, including concepts of action-reaction pairs and work done on the spring.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about how the forces exerted on different bodies (the spring and the person) can be balanced.
  • Another participant clarifies that the forces do not need to be balanced since they act on different bodies, and the spring's compression may lead to acceleration of the person if friction is absent.
  • A participant seeks clarification on whether there are two forces acting on the person: one from the spring and another from their own force exerted on the spring.
  • One response indicates that there is indeed a force from the spring on the person, but questions the usefulness of the term "reaction" in this context.
  • Another participant mentions that the forces involved in the interaction between the person and the spring are equal and opposite, but questions the necessity of these forces being equal in the context of action-reaction pairs.
  • A later reply asserts that the forces are indeed a pair describing one interaction, suggesting a potential disagreement about the nature of these forces.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the forces acting on the person and the spring must be equal to satisfy the action-reaction criteria. There are competing views on the interpretation of these forces and their implications.

Contextual Notes

Participants discuss the calculation of work done on the spring, noting that if the force is not constant, integration may be necessary. There is also mention of the need for calculus knowledge to fully understand the work done by elastic forces.

Aldnoahz
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Hi all, I am quite confused by the forces relating to a horizontlly placed spring when someone directly exerts a force to the compress it. If I exert a force F to the right to compress the spring, which, say, is placed against a wall, the spring exerts an elastic force on me but I don't see how these two forces are related because they are exerted on different bodies. How can they be balanced out if they act on different bodies?

Let me thank you in advance. I have been bothered by this problem for a while.
 
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They don't have to be balanced. As you say, they act on different bodies so their effects may be different. The spring gets compressed and you may get some acceleration from this force unless there is friction to balance the effect of the spring on you.
 
nasu said:
They don't have to be balanced. As you say, they act on different bodies so their effects may be different. The spring gets compressed and you may get some acceleration from this force unless there is friction to balance the effect of the spring on you.

Thank you for replying. I just want some clarification. If I analyze the horizontal forces on me (assume no friction), are there two forces? One from the compressed spring and the other from the reaction force by me pushing the spring with the force F?

If I do work by exerting this force F to compress the spring, how do you calculate the work done by using force times distance formula?
 
There is one force from the spring on you. You can call it the reaction to you r force on the spring but the "reaction" is not a very useful concept.
There is the interaction between you and the spring (two bodies) and this results in a pair of equal and opposite forces, each one acting on one of the two bodies.

You don't if the force is not constant. You need to integrate over the distance. Or just read about work of elastic force and use the formula, if you did not learn calculus yet.
 
nasu said:
There is the interaction between you and the spring (two bodies) and this results in a pair of equal and opposite forces, each one acting on one of the two bodies.

But the two forces don't have to be equal; how can they satisfy the "this results in a pair of equal and opposite forces" criteria to be action-reaction pair?
 
Aldnoahz said:
But the two forces don't have to be equal; how can they satisfy the "this results in a pair of equal and opposite forces" criteria to be action-reaction pair?
Yes, they are. They are a pair of forces describing one interaction.
 

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