Question

Where does the negitive come from?

Answer 1

Heres a pic

Answer 2

Clockwise direction is defined as negative.

Answer 3

wouldn't it be easier to set clockwise as positive?

Answer 4

since the force is pointing to the right...

Answer 5

Hey Cliff, thanks. I understand that but I don't see it. How can I determine when the movement is goign clockwise or not?

Answer 6

You look at the two sources of torque.
Decompose the force and lever arm into clockwise and counterclockwise directions.
You can call whatever direction you want positive or negative.

Answer 7

i believe they call it "vanigron's theorem" yes?

Answer 8

Well, F in the Y direction should be pointing up, and F in the X direction should be pointing right. But I see don't see why or how hte force move in oposite direction beven when breaking up into components.

Answer 9

@lgbasallote , never heard of that theorem.

Answer 10

hmm...if you put CCW as positive...then both should be both negative...right?

Answer 11

Look at the horizontal and vertical components of force relative to the pivot point.

Answer 12

CCW is positive because of how we define angles from the unit corcle.

Answer 13

vanigron's theorem states that when you have a moment of force along a certain point, it's equal to the sum of the moment of its components along the same point

Answer 14

ah yes. nevermind what i said

Answer 15

along a point?

Answer 16

i don't have it memorized

Answer 17

the point is moment of force is equal to moment of Fy + moment of Fx

Answer 18

you'll understand when you get older...

Answer 19

Haha, I got my engineering degree 10 years ago.

Answer 20

then it's 10 years more

Answer 21

Cliff, you're the man. I'm still not seeing it but maybe with more research it will be more apparent. I'm goign to try to draw a picture and reatach.

Answer 22

This is a pretty simple problem using basic engineering statics.
The force is parallel to the 6in. lever arm, so their using the 3-4-5 triangle to decompose the force into components perpendicular and parallel to that 6in. arm.

Answer 23

I know the relation you're talking about @lg, just never heard it called Vanigron's Theorem before. And I was just confused by the phrasing of "along a point" since points don't have length.

Answer 24

i hate math...what do you expect....

Answer 25

;-)

Answer 26

If I were doing it, I'd rather find the total lever arm from the pivot to the application of force, then decompose into horizontal and vertical. It might be less elegant, but easy to see using basic principles.

Answer 27

I actually tried to use cartesian coordinates first and use the cross product. Still, I was wrong. I keep messing up on determining what is negative. And yes, its statics

Answer 28

positive or negative is your choice.
By convention, clockwise is usually negative.

Answer 29

This is how I see it.