# The difference of bulk and young modulus

1. Feb 16, 2009

### saray1360

Hi everyone,

I want to know what the difference between bulk modulus and young modulus is? In some papers, it seems that they have compared the value of these two as if they are the same.

Could anyone help me with this regard?

Regards,
Sara

2. Feb 16, 2009

Youngs modulus refers to stretching and bulk modulus refers to compressing.

3. Feb 16, 2009

### saray1360

it is not the answer, sorry

4. Feb 16, 2009

Youngs modulus and bulk modulus are different..The former is tensile stress/tensile strain the latter is bulk stress/bulk strain.

5. Feb 16, 2009

### Mapes

The bulk modulus K is the amount of pressure required to obtain a certain change in volume per unit volume. The Young's modulus is $E=3(1-2\nu)K$ (*). For a rod (long, thin geometry), it is the amount of axial stress (compression or tension) required to obtain a certain change in axial length per unit length. They are approximately equal when $\nu$ is near 0.33, which is common for metals (but not for ceramics or elastomers).

(*) $\nu$ is Poisson's ratio, the ratio of the lateral contraction over the axial contraction for a rod under axial load.

EDIT: Removed unnecessary comment.

Last edited: Feb 16, 2009