Calculating Moments About a Point

  • Thread starter Thread starter Bolter
  • Start date Start date
  • Tags Tags
    Moments Point
Click For Summary

Homework Help Overview

The discussion revolves around calculating moments about a point, specifically focusing on the signs assigned to moments based on their direction (clockwise or counter-clockwise) and the contributions of different forces.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the assignment of positive and negative values to moments based on their rotational direction. Questions arise regarding the effects of specific forces (##F_x## and ##F_y##) on the rotation of the object.

Discussion Status

Some participants have provided feedback on the original poster's reasoning, with one noting that the approach to defining moments seems acceptable. However, there are ongoing questions about the correctness of the units in the final answer and the interpretation of the forces' effects on rotation.

Contextual Notes

Participants are discussing the implications of their assumptions regarding the direction of moments and the forces involved, indicating a need for clarity on these definitions.

Bolter
Messages
262
Reaction score
31
Homework Statement
See below
Relevant Equations
moment = force x perpendicular distance
Not sure if I answered this question right

Screenshot 2020-10-11 at 23.19.42.png

IMG_5352.JPG


I took my clockwise moments as +ve and counter-clockwise moments as -ve

Any help would be much appreciated! Thanks
 
Physics news on Phys.org
Should ##F_x## be positive or negative?

Are you sure you took clockwise as positive for the moments? Does ##F_y## tend to rotate the object clockwise or counterclockwise?
 
  • Like
Likes   Reactions: Lnewqban
TSny said:
Should ##F_x## be positive or negative?

Are you sure you took clockwise as positive for the moments? Does ##F_y## tend to rotate the object clockwise or counterclockwise?

Oh it looks like Fy is trying to rotate the bar counter-clockwise
whereas Fx is also rotating it counter-clockwise?

so let's say I took counter-clockwise to be a positive moment, then the moment about O is (Fx * 0.15) + (Fy * 1.5) = 3.74 kN?
 
  • Like
Likes   Reactions: PhanthomJay
It looks OK to me.
 
Bolter said:
Oh it looks like Fy is trying to rotate the bar counter-clockwise
whereas Fx is also rotating it counter-clockwise?
Yes

so let's say I took counter-clockwise to be a positive moment, then the moment about O is (Fx * 0.15) + (Fy * 1.5) = 3.74 kN?
Looks good except for the units of the answer.
 
  • Like
Likes   Reactions: Lnewqban

Similar threads

  • · Replies 6 ·
Replies
6
Views
1K
  • · Replies 40 ·
2
Replies
40
Views
6K
  • · Replies 27 ·
Replies
27
Views
3K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 24 ·
Replies
24
Views
2K
  • · Replies 12 ·
Replies
12
Views
4K
  • · Replies 3 ·
Replies
3
Views
1K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 105 ·
4
Replies
105
Views
5K
  • · Replies 2 ·
Replies
2
Views
749