Direction of Moment: 1200N at A- Clockwise or Counterclockwise?

[goldfish9776]

Homework Statement

Why shouldn't the direction of moment for 1200n at A =clockwise? Why the book gave counterclockwise?

Homework Equations

The Attempt at a Solution

 

[stockzahn]

It depends if you are talking about the moment of the force (1200 N), which is turning clockwise or if you are looking at the reaction moment in the connection of the beam to the wall (M_A), which has to turn counterclockwise to establish the equilibrium. Two moments of the same size in two different directions.

EDIT: Sorry, I didn't look at the drawing well: The moment M_A of course must be the sum of the moments produced by the force (1200 N) and the weight of the beam (both with clockwise direction).

 

[haruspex]

EDIT: Sorry, I didn't look at the drawing well: The moment MA of course must be the sum of the moments produced by the force (1200 N) and the weight of the beam (both with clockwise direction).

Well, no, as you wrote in the first paragraph M_A would be equal and opposite to the sum of those two moments, hence anticlockwise.
Anyway, it really doesn't matter which way it is presumed to be. M_A could be taken to be clockwise, and the equations written accordingly. It would then turn out to have a negative value.

 

[goldfish9776]

the correct

Well, no, as you wrote in the first paragraph M_A would be equal and opposite to the sum of those two moments, hence anticlockwise.
Anyway, it really doesn't matter which way it is presumed to be. M_A could be taken to be clockwise, and the equations written accordingly. It would then turn out to have a negative value.

the correct moment would be in clockwise direction , right ? the anticlockwise in merely the reaction of the moment produced which is in opposite direction , am i right ?

 

[stockzahn]

[] ... M_A would be equal and opposite to the sum of those two moments, hence anticlockwise.

That was what I meant to say in my EDIT. Sorry for the ambigous expression.

 

[haruspex]

the correct moment would be in clockwise direction , right ? the anticlockwise in merely the reaction of the moment produced which is in opposite direction , am i right ?

In the textbook extract you posted, M_A is the reaction moment. Read it carefully. There is no error there.