Re: what is the difference between hardness, elasitc molulus?

All these terms are discussed in a Materials Science text book and are 
fairly well covered in the following Wikipedia links.  Read up.

Elastic Modulus http://en.wikipedia.org/wiki/Elastic_modulus

Hardness http://en.wikipedia.org/wiki/Hardness

Tensile strength http://en.wikipedia.org/wiki/Tensile_strength http://www.absoluteastronomy.com/topics/Tensile_strength

Elastic modulus is the slope of the linear stress-strain curve with no 
deformation of the material.  Tensile is the force per unit area necessary 
to deform or break the material. Hardness is a measurement of the distance 
a specific indentor penetrates into a material with a known force.  
Hardness and tensile strength are linearly related so hardness can be used 
as a fast measurement of tensile on the same materials.  Since the 
measurements are all force on unit areas the units are usually Pascals
[newtons/sq.m] or PSI[lbs/sq. in] altho hardness values are usually 
expressed in a scale from the specific machine used to test.