# Homework Help: Shear formula

1. Nov 25, 2016

### fonseh

1. The problem statement, all variables and given/known data
In the notes, the author stated that the shear stress is constant over the bottom face of the segment ... why in figure 7-4 , we can see that the shear stress varies ?

2. Relevant equations

3. The attempt at a solution
Which is correct ? The red circled part or the figure ?

#### Attached Files:

File size:
221.4 KB
Views:
95
• ###### shear fromula 2.PNG
File size:
58.1 KB
Views:
86
2. Nov 26, 2016

### PhanthomJay

They are both correct, the Profile view shows the shear stress at the bottom, constant across the width t, the other views show the varying bending stresses , not shear stresses, but if you look carefully in the 3D view you will find the constant longitudinal shear stress at the bottom of the plane ( $\tau$)

3. Nov 26, 2016

### fonseh

what do you mean by the other view here ? the figure 7-4 (b) in the first photo ?

4. Nov 26, 2016

### fonseh

shear stress at the bottom plane ?
In the profile view , we could see that the stress ( i am not sure bending stress or shear stress) varies linearly .... But , you said it's constant across the width ? I'm confused

5. Nov 26, 2016

### PhanthomJay

You should have long learned about bending stresses before tackling distributed shear stress. Figure 7.4b shoes the bending stress varying from max compression to 0 from top to NA, then up to max tension at bottom. Shear stress is shown in fig 7,4c as constant at the bottom across the thickness, t.

6. Nov 26, 2016

### fonseh

so , in figure 7.4 b , the figure shown is the bending stress across the vertical length of beam ?

7. Nov 27, 2016

### PhanthomJay

Yes, My/I bending stresses.