Youngs Modulus and Elastic Modulus

In summary, the difference between Young's Modulus and Shear Modulus is that Young's Modulus is specifically for linear expansion/compression, while the Shear Modulus relates how the top layer of a material will move in relation to the bottom layer.
  • #1
Poppy
3
0
I am doing my A2 physics coursework of the bending of cantilevers [zz)] I hung masses on a steel bar and measured the deflection, and then used a formula to calculate the Youngs Modulus of the steel, but the answer I got was way out - 9.6X10^9 instead of 200X10^9. Is this because I calculated the Elastic Modulus instead of the Youngs Modulus? What is the difference between the two?
 
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  • #2
I'm not familiar with the term "elastic modulus." Do you mean elastic constant (as in spring constant) or coefficient of elasticity?
That last one is the percentage of the original speed (or is it kinetic energy?) that an object will keep after a collision. But I don't think this is ever referred to as a "modulus."

I think that the two terms are one and the same. The reason (probably) that your numbers did not work, is that the amount of bend depends on the "shear modulus." Young's is specifically for linear expansion/compression. Sideways strain requires one side of an object to stretch whil the other side compresses.
 
  • #3
Thankyou for your help. Could you please clarify the difference between Youngs Modulus and Shear Modulus? Can I find a recorded value for the shear modulus of steel or is this not a property of the material?
 
  • #4
There are genreally three types of "moduluses" (moduli?) Young's Modulus, bulk modulus and shear modulus.

All three are properties of the material from which the object is made. All three are usually provided in a table in nearly all texbooks. Young's Modulus (Y) is determined by how much object's length will change when subjected to stress.

Bulk modulus (beta) is determined by how the volume of the object will change when subjected to changes in pressure.

Shear modulus is harder to talk about, but easiest to demonstrate: take a thick stack of paper (like a phone book) and with your hand on the top, push horizontally. THe layers of the stack will shear and the top of the stack will move while the bottom stays put. All objects can be thought of as layers of material. HOw easily will these layers separate from each other? THe shear modulus relates how the top layer of a material will move in relation to the bottom layer.

Whenever something is bending , the material is shearing some amount because the inside of the bend gets compressed while the outside of the bend gets stretched. "Layers" of the material have to move laterally to each other.
 
  • #5
Originally posted by Poppy
Is this because I calculated the Elastic Modulus instead of the Youngs Modulus? What is the difference between the two?


Young's Modulus is also referred to as the Modulus of Elasticity. They are the same thing.
 
  • #6
Is the Shear Modulus also known as the Bending or Flexural Modulus? Because the formula I used was from a website which called it that, but I thought it was the same as the Youngs Modulus. Silly me.
 
  • #7
Whoops. LOng weekend.

I'm not certain about that. I never heard of "flexural" modulus. It has been a long time since I did stress/strain, and unfortunately it is not part of any course that I teach.

I am certain that the shear modulus is used to determine "flex" but I seem to recall that the formula in which it is used is slightly different than the one used for simple "shearing." So a "flexural" modulus might be a variation of the shear modulus.

I would take this question to the engineering section of the forum for further information.
 

What is Young's Modulus and Elastic Modulus?

Young's Modulus and Elastic Modulus are both measures of a material's stiffness or ability to resist deformation under stress. They are often used interchangeably, but technically, Young's Modulus is a specific type of Elastic Modulus that measures the ratio of stress to strain in a material.

How is Young's Modulus and Elastic Modulus calculated?

Young's Modulus is calculated by dividing the stress (force per unit area) by the strain (ratio of the change in length to the original length) in a material. Elastic Modulus can be calculated using different methods, depending on the type of stress and strain being measured. For example, shear modulus measures the ratio of shear stress to shear strain, while bulk modulus measures the ratio of hydrostatic stress to volumetric strain.

What units are used to measure Young's Modulus and Elastic Modulus?

Young's Modulus and Elastic Modulus are typically measured in units of pressure, such as pascals (Pa) or pounds per square inch (psi). In some cases, they may also be measured in units of energy, such as joules per cubic meter (J/m3) or foot-pounds per cubic inch (ft-lb/in3).

How do Young's Modulus and Elastic Modulus affect a material's properties?

The higher the Young's Modulus or Elastic Modulus of a material, the stiffer and more resistant to deformation it is. This means that materials with high Modulus values are stronger and more able to withstand forces without bending, stretching, or breaking. However, materials with lower Modulus values may be more flexible and able to absorb energy without fracturing.

What are some common applications of Young's Modulus and Elastic Modulus?

Young's Modulus and Elastic Modulus are used in a wide range of industries and applications, including construction, engineering, and materials science. They are essential in designing structures and products that can withstand the forces and stresses they will encounter in their intended use. They are also important in understanding the behavior of materials under different conditions, such as temperature, pressure, and strain.

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