Why do we use negative signs for clockwise moments in torque calculations?

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The discussion revolves around the calculation of torque and the use of negative signs for clockwise moments. The user struggles with understanding how the total torque can be 19.08 Nm clockwise, despite calculating individual moments from forces incorrectly. It is clarified that only the perpendicular distance to the line of force matters in torque calculations, not the total distance traveled. Additionally, the convention of labeling clockwise moments as negative is explained, emphasizing the importance of distinguishing between clockwise and anticlockwise torques when both are present. The conversation highlights the need for clarity in educational materials regarding torque conventions.
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I'm stuck on this problem at the moment.
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The answer is 19.08 nm clockwise but i just don't see how it can be.

Check this.

2.8x(0.8+5.5)= 17.64 nm

If I use the 4.6 it ends up
4.6x(0.8+5.5) = 28.98 nm

I don't get how it can be 19.08 clockwise when there is only one force going clockwise or anticlockwise. That moment from that force isn't 19 though.
 
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The moment due to the 2.8 N force is (2.8)(5.5)= 15.4 Nm (The force is multiplied by the length of the arm perpendicular to the force). The moment due to the 4.6 N force is (4.6)(0.8)= 3.68 Nm for a total of 15.4+ 3.68= 19.08 Nm
 
HallsofIvy said:
The moment due to the 2.8 N force is (2.8)(5.5)= 15.4 Nm (The force is multiplied by the length of the arm perpendicular to the force). The moment due to the 4.6 N force is (4.6)(0.8)= 3.68 Nm for a total of 15.4+ 3.68= 19.08 Nm


I don't get how that would work. The 2.8 Force would have to go through 0.8m distance to get to point A.
 
mechanicstudy said:
I don't get how that would work. The 2.8 Force would have to go through 0.8m distance to get to point A.
No, only the perpendicular distance matters. (The distance perpendicular to the line of force.) As far as the 2.8 N force is concerned, that 0.8m distance could be 800m and it would make no difference. Read this: http://hyperphysics.phy-astr.gsu.edu/hbase/torq.html" (Torque is another name for moment.)
 
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Finally i get it. Ok i got a questions to ask.

1: When does clockwise become negative? When i look at the notes i have been given. Sometimes its negative and sometimes it's not. Does it only become negative when an Anticlockwise force is present?

thanks by the way.
 
mechanicstudy said:
1: When does clockwise become negative? When i look at the notes i have been given. Sometimes its negative and sometimes it's not.
Calling clockwise moments negative is just the standard convention. Often you only care about the magnitude of the torque, so the direction doesn't matter.
Does it only become negative when an Anticlockwise force is present?
You must distinguish anticlockwise from clockwise torques when both are present, and using the standard sign convention is a great way to do that.
 
Doc Al said:
Calling clockwise moments negative is just the standard convention. Often you only care about the magnitude of the torque, so the direction doesn't matter.

You must distinguish anticlockwise from clockwise torques when both are present, and using the standard sign convention is a great way to do that.

thank you. My notes just seem to neglect information like that and it has left me confused.
 
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