Moment of force about a point

  • Thread starter BigJon
  • Start date
  • #1
24
0

Homework Statement



The moment of force Fa about point O

Homework Equations





The Attempt at a Solution



I know how to setup with breaking the force into x,y component but how to tell if its rotating cw or ccw about the point. I think y is ccw but i cant tell on x. I think i would use right hand rule but need to know how to do it correctly.

Homework Statement





Homework Equations





The Attempt at a Solution

 

Attachments

Answers and Replies

  • #2
93
3
Right hand rule would work here. How did you come to conclusion that Fy
"rotates" ccw? If You know the distance and direction of the force, it's easy to determine the direction of moment.

The distance has to be perpendicular to the force, and your fingers have to be directed in the direction of the force, i.e. the direction of rotation. Your palm shows moment direction.
 
  • #3
24
0
Well to setup the prob it would be like -200cos(60)(9in)+200sin(60)(30in), but why is the first term negative if x pulls straight out? My prof. didnt pull this from the book. Maybe I'm not understanding the principle behind moments etc.
 
  • #4
93
3
Well to setup the prob it would be like -200cos(60)(9in)+200sin(60)(30in), but why is the first term negative if x pulls straight out? My prof. didnt pull this from the book. Maybe I'm not understanding the principle behind moments etc.
Please check the photo that i attached. If you try to rotate Fx around point P, your thumb would be faced down which is the negative z direction, and therefore that moment is also negative.
 

Attachments

Related Threads on Moment of force about a point

  • Last Post
Replies
3
Views
3K
  • Last Post
Replies
1
Views
900
Replies
2
Views
19K
Top