Why is the weight going upward? Statics

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Discussion Overview

The discussion revolves around the interpretation of forces in a statics problem, specifically why the weight is represented as acting upward in a free body diagram (FBD) instead of downward. The scope includes homework-related queries and technical explanations regarding force representation in statics.

Discussion Character

  • Homework-related, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions why the weight is depicted as pointing upwards rather than downwards, suggesting there might be another force, Fae, acting upwards.
  • Another participant proposes that W is simply used to represent the force acting in the vertical chain connected to point A.
  • A different participant notes that W is defined as mg, where m = 200kg, expressing confusion over this representation.
  • One participant acknowledges the upward direction of W but speculates that this might be to ensure a positive answer in calculations, indicating a concern about the implications of negative forces.
  • Another participant clarifies that W points upward in the FBD of joint A because the chain applies an upward force, equating Fae to W.
  • One participant asserts that W must represent tension in the string, dismissing other interpretations.

Areas of Agreement / Disagreement

Participants express differing views on the representation of forces, with no consensus reached on the reasoning behind the upward direction of weight in the problem.

Contextual Notes

Participants discuss the implications of force direction on calculations and the representation of forces in free body diagrams, but there are unresolved assumptions regarding the definitions and roles of the forces involved.

asz304
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Homework Statement



http://www.engr.mun.ca/~neil/1010/prob11/set2.pdf"

In the first problem in the link above, why is the weight pointing upwards instead of downwards? I thought there will be a different force prolly called Fae pointing upwards with the weight pointing downwards.

Thanks
 
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In the first part I think they just used W to represent the force acting in the vertical chain connected to A.
 
But in the calculations, W = mg, where m = 200kg. I still don't get it...
 
Yeah I see it now. Not too sure why exactly they did that other than to get a positive answer. If you had W acting downwards, then you'd get the two forces to be negative meaning that the forces act in the opposite direction.
 
asz304: W points upward in the FBD of joint A because chain AE applies an upward force on point A, called Fae, where Fae = W. If you wish to write vector Fae, that is fine. And the magnitude of vector Fae is W; i.e., Fae = W.

By the way, always leave a space between a numeric value and its following unit symbol. E.g., 200 kg, not 200kg. See the international standard for writing units[/color] (ISO 31-0[/color]).
 
W must mean Tension in the string. It can't be anything else.
 

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