Why Do We Multiply Distance, Mass, and Gravity in Sum of Forces Calculations?

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Discussion Overview

The discussion revolves around the reasoning behind the formula used to calculate weight and the sum of forces in a specific context, particularly in relation to a problem involving a pipe with mass. Participants explore why distance, mass, and gravity are multiplied in certain calculations rather than simply summing forces.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant notes the formula for weight as W=mg and questions why the sum of forces involves multiplying distance, mass, and gravity.
  • Another participant clarifies that the pipe's mass is given as 12 kg per meter, suggesting that this affects the calculation.
  • A follow-up question is posed regarding the implications of using a total mass of 12 kg versus a mass per unit length.
  • A participant raises a question about the calculation of moments, specifically why a certain multiplication does not seem to apply in their context.
  • Another participant explains that the forces applied are at a specific distance from the axis and that the moments produced by these forces cancel each other out.

Areas of Agreement / Disagreement

The discussion contains multiple viewpoints regarding the application of formulas in the context of the problem, and participants do not reach a consensus on the reasoning behind the calculations.

Contextual Notes

Participants reference specific problem statements and conditions that may affect the calculations, but these assumptions and dependencies are not fully resolved within the discussion.

Marchese_alex
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Ok, so the formula I know to find weight is W=mg. Why is it that when doing a sum of forces in z they multiply (distance)(mass)(gravity) and not simply sum the gravity force that is mg?
 

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Because the pipe has a mass of 12 kg per meter of length. Read the problem statement carefully.
 
SteamKing said:
Because the pipe has a mass of 12 kg per meter of length. Read the problem statement carefully.

ooohh... so if it said only 12 kg, then I would only use mg?
 
why when calculating sum Mx=0 isn't (60)(.4)(.2)? isn't moment=force time the distance to where the moment is being taken?
 
Last edited:
The 60 N forces are applied 400 mm from the x-axis. There are two 60 N forces acting in opposite directions. The moments produced by these forces about the x-axis cancel out.
 

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