# Homework Help: Restriction or rotation

1. Oct 24, 2015

### werson tan

1. The problem statement, all variables and given/known data
in this diagram , we know that the whole thing wouldnt rotate about y and z axis , right ? why the sign of prevention of rotation are not shown there ?
i added green sign = prevent rotation in the z axis , red = prevent rotation in the y axis

2. Relevant equations

3. The attempt at a solution

#### Attached Files:

• ###### Untitled.png
File size:
193.7 KB
Views:
65
2. Oct 24, 2015

### haruspex

Not sure what you mean by "sign of prevention of rotation". You seem to have added torques, maybe opposing rotation at B and C. Is that what you mean, that you think there should be torques there for equilibrium?

3. Oct 24, 2015

### werson tan

I'm wondering why there are no moment restriction about y and z -axis .....
from the first sight , we know that the whole structure wouldnt turn in any direction , right ?

4. Oct 24, 2015

### haruspex

Yes, but that can be explained entirely in terms of the linear forces shown in the second diagram.

5. Oct 24, 2015

### werson tan

Can yo
Can you explain figure 2??

6. Oct 24, 2015

### haruspex

What is it that puzzles you about it? It shows the linear forces at each of the three bearings, resolved into the coordinate axes.

7. Oct 24, 2015

### werson tan

the whole structure cant rotate in x , y , and z direction right ? why the restriction of moment about y, and z axis are not shown ? only x direction(45Nm) is shown .....this puzzled me....

8. Oct 24, 2015

### haruspex

The curved arrow around the x axis is not a restriction of motion, it is an applied torque. Why would you expect symbols indicating a restriction of motion? I've never seen such.
Edit: do you mean reaction forces and torques?

9. Oct 24, 2015

### werson tan

since the structure cant turn about x , y, and z axis ... so , there should be signs to indicate the moment restrictions about x , y and z axis , right ... just like this case...

#### Attached Files:

• ###### DSC_0128[1].JPG
File size:
33.7 KB
Views:
55
10. Oct 24, 2015

### haruspex

Those are not moment restrictions. The 200Nm is an applied torque. The MAx and MAz are unknown moments to be determined.
I have never seen a diagram in which 'moment restrictions' are indicated, and I'm not sure what the term would mean. Rotation about an axis is prevented by the moments of the forces. There is no deity edicting "thou shalt not turn".

11. Oct 24, 2015

Ol
Ok!