Young's Modulus - estimate elastic limit

In summary, the conversation is about estimating the elastic limit of a wire for a homework assignment on Young's Modulus. The question asks for the mass at which the elastic limit is reached, but it is clarified that the elastic limit is actually the stress at yield in N/m^2. The graph being used plots mass (in kg) versus extension (in mm). The process to calculate the stress at yield is explained as obtaining the applied force by multiplying the mass by 9.81 (acceleration due to gravity) and dividing by the cross sectional area of the wire in meters. The final answer will be in units of N/m^2 or pascals.
  • #1
ZedCar
354
1

Homework Statement




I'm completing a homework for Young's Modulus and one question asks to estimate the elastic limit for the wire which was used.

I can see where this approximately is on the graph I have drawn. When the question asks to estimate the elastic limit, does this mean to simply state the mass which was applied when the elastic limit was reached?

Thanks
 
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  • #2
I had another think about it. Would I be right in thinking the elastic limit would be the mass where this happens (in kg) multiplied by gravitational acceleration and the result of this multiplication stated in Newtons?
 
  • #3
No, the elastic limit is the stress at yield (yield stress of the wire, in N/m^2, or Pascals), not the force at yield. What are you plotting on your graph?
 
  • #4
Thanks PhanthomJay, it's mass / grams on the y-axis and extension / mm on the x-axis.
 
  • #5
ZedCar said:
Thanks PhanthomJay, it's mass / grams on the y-axis and extension / mm on the x-axis.
Looks then like your plotting mass (presumably a mass hanging down on the wire, yielding a weight/force unit) versus extension.. You want to find the stress at yield. What is it? Are the properties of the wire given?
 
  • #6
PhanthomJay said:
Looks then like your plotting mass (presumably a mass hanging down on the wire, yielding a weight/force unit) versus extension..

Yes, that's right.

PhanthomJay said:
You want to find the stress at yield. What is it? Are the properties of the wire given?

Ah, I see what you mean! I need to find the stress at the yield point.

So I'll obtain the applied force by using the mass (in kg) at which the elastic limit is reached and multiply this by 9.81 (acceleration due to gravity). Then divide this number by the cross sectional area of the wire. Ensuring when calculating the cross sectional area of the wire the diameter is in the SI unit of the metre.

So the final figure for the estimation of the elastic limit would be in the units of N/m2
 
  • #7
ZedCar said:
Yes, that's right.



Ah, I see what you mean! I need to find the stress at the yield point.

So I'll obtain the applied force by using the mass (in kg) at which the elastic limit is reached and multiply this by 9.81 (acceleration due to gravity). Then divide this number by the cross sectional area of the wire. Ensuring when calculating the cross sectional area of the wire the diameter is in the SI unit of the metre.

So the final figure for the estimation of the elastic limit would be in the units of N/m2
Yes, excellent. And I'm sure you know that a N/m^2 is called a 'pascal' for short.
 
  • #8
PhanthomJay said:
Yes, excellent. And I'm sure you know that a N/m^2 is called a 'pascal' for short.

Yes, thanks very much!
 

1. What is Young's Modulus?

Young's Modulus, also known as the elastic modulus or modulus of elasticity, is a measure of the stiffness of a material. It is defined as the ratio of stress (force per unit area) to strain (change in length per unit length) when a material is subjected to an external force. It is typically denoted by the symbol E and is expressed in units of pressure, such as pascals (Pa) or pounds per square inch (psi).

2. How is Young's Modulus measured?

Young's Modulus is typically measured using a tensile test, where a sample of the material is pulled in opposite directions until it reaches its breaking point. The amount of force applied and the resulting change in length are recorded, and Young's Modulus is calculated using the equation E = stress/strain.

3. What is the significance of Young's Modulus?

Young's Modulus is an important material property that helps engineers and scientists understand how a material will behave under different types of stress. It is used in the design and analysis of structures and components, as well as in the development of new materials. It also plays a crucial role in determining the elastic limit, or the maximum stress a material can withstand without permanently deforming.

4. Can Young's Modulus change for a material?

The value of Young's Modulus can vary for different materials and can also change under certain conditions. Factors such as temperature, strain rate, and microstructure can affect the modulus of a material. Additionally, some materials exhibit anisotropic behavior, meaning their modulus may vary in different directions.

5. How is Young's Modulus used in material selection?

Young's Modulus is an important consideration in material selection for different applications. It can help determine if a material is suitable for a specific use based on its stiffness and ability to resist deformation. For example, materials with a high modulus are ideal for load-bearing structures, while those with a lower modulus may be better suited for applications that require flexibility.

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