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

AI Thread Summary
The discussion centers on the calculation of weight and forces in physics, specifically addressing why the formula W=mg is expanded to include distance when calculating the sum of forces. It clarifies that when dealing with objects like a pipe with mass per unit length, the total weight must account for the entire length of the pipe, hence the multiplication of distance, mass, and gravity. The conversation also touches on the calculation of moments, noting that the forces applied at a distance from the axis create moments that can cancel each other out. The importance of carefully reading problem statements to determine whether to use total mass or mass per unit length is emphasized. Understanding these principles is crucial for accurate force and moment calculations in physics.
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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