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

[Marchese_alex]

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?

 

[SteamKing]

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

 

[Marchese_alex]

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?

 

[Marchese_alex]

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?

 

[SteamKing]

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.