# B A statistical definition of Young's Modulus?

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1. Oct 20, 2016

### Metals

Young's Modulus is usually defined as the intrinsic property of a material indicating it's stiffness, or it's ability to resist deformation. Though, it is measured in Pa, meaning it should have some statistical description. Spring constant, for example, can be define as the stiffness of an item and is known as the number of newtons to extend the item by a metre.

Upon discussing with a teacher, I believe he provided me with a sufficient explanation. Although, we both want confirmation on whether this is generally accepted as true or not:

Young's Modulus = Stress/Strain
Stress = Force/Area(cross-sectional)
Strain=Δlength/length

If we make stress equal to 1, then the length of the item has been doubled due to a force extending it by its original length. This way, Young's Modulus can be defined as the amount of force across a metre squared of a material required to extend the material by its original length.

Everyone agree?

2. Oct 20, 2016

### Dr. Courtney

Nope. Most materials are not elastic over strains that large.

Young's modulus can only be defined as a constant over strains small enough for the material response to be linear.

3. Oct 20, 2016

### Staff: Mentor

In addition to what Dr. Courtney said, even if the linear behavior could extend to twice the original length, the algorithm you gave is still not correct. The strain is equal to the stress divided by Young's modulus, and Young's modulus is very large, so the calculated strain would be very small.

4. Oct 20, 2016

### lychette

Yep....this is not a stupid idea I use it (FOR EFFECT) in my teaching ! For someone LEARNING about Youngs modulus the numbers are formidable..Massive forces for minute extensions.(boring sir !)
However...If you take a 1m3 of steel then the Youngs modulus represents the force needed to cause an extension of 1m (IF SUCH A THING WAS POSSIBLE WITHOUT WORRYING ABOUT WHY IT IS NOT POSSIBLE) to the cube. This certainly illustrates the high value of youngs modulus for steel and....it is interesting to stretch the imagination !
The joys of linear or non-linear behaviour can come later

5. Oct 20, 2016

### Staff: Mentor

Only if the units of force are the same as Young's modulus times m^2.

6. Oct 20, 2016

### lychette

Took you a long time to spot that :)

7. Oct 20, 2016

### Staff: Mentor

I was taking a nap.

8. Oct 20, 2016

### lychette

respect....so was I

9. Oct 20, 2016

### Staff: Mentor

Huh? Why do you think that?