# When calculating the shear stress, what should the area be?

## Homework Statement

I'm looking at some problems and solutions to them, and when they calculate shear stress instead of having the area of the thing be pi*r^2, there is usually a (pi/4)*r^2.

## Homework Equations

Shear Stress = V/A

## The Attempt at a Solution

I don't understand where they get the 1/4 in the denominator.

## Answers and Replies

SteamKing
Staff Emeritus
Homework Helper
You might want to review how shear stress is calculated. Your formula is not the usual one.

You might want to review how shear stress is calculated. Your formula is not the usual one.
I'm using and reading the chapter of shear stress in the book. That is what it tells me that shear stress is... Unless, I'm missing something.

PhanthomJay
Homework Helper
Gold Member
The cross section area of a circular rod is (pi)(r^2) OR (pi)(d^2)/4

The cross section area of a circular rod is (pi)(r^2) OR (pi)(d^2)/4

Yeah, I figured it out. They gave the diameter in the problem so it was pi (d/2)^2. which is pi*(d^2)/4. I was stumped, but luckily i understand.

THANKS!