Young's Modulus?

[MrNeuro]

An increase in the cross-sectional area of a typical human bone would most likely:
A. decrease the Young's modulus for that bone, because the stress would be decreased.
B. increase the Young's modulus for that bone, because the strain would be decreased.
C. not affect the Young's modulus for that bone, but the strain for any given stress would be decreased.
D. not affect the Young's modulus for that bone, but the strain for any given stress would be increased.

Answer (highlight to see): C

HUHHHHHHH?????

why doesn't young's modulus change i thought

E= (F/A)/ (dL/Lo) hence E is inversely proportional to A

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[MedPR]

An increase in the cross-sectional area of a typical human bone would most likely:
A. decrease the Young's modulus for that bone, because the stress would be decreased.
B. increase the Young's modulus for that bone, because the strain would be decreased.
C. not affect the Young's modulus for that bone, but the strain for any given stress would be decreased.
Correct Answer
D. not affect the Young's modulus for that bone, but the strain for any given stress would be increased.

Answer (highlight to see): C

HUHHHHHHH?????

why doesn't young's modulus change i thought

E= (F/A)/ (dL/Lo) hence E is inversely proportional to A

You might want to edit out "Correct Answer" under answer C. It's kind of a giveaway

Isn't young's modulus a constant for any material at a given temperature? So if you increase cross sectional area, you decrease stress. For young's modulus to stay constant, strain must also be decreased.

 

[pfaction]

I don't get it, MedPR.

Delta L = FL0/EA; so E and A should be proportional, no?

 

[MrNeuro]

You might want to edit out "Correct Answer" under answer C. It's kind of a giveaway

Isn't young's modulus a constant for any material at a given temperature? So if you increase cross sectional area, you decrease stress. For young's modulus to stay constant, strain must also be decreased.

LOOOL thanks...

ahhh i didn't know that and what's even more annoying is i just reread that chapter
ugghhhhh TY

 

[MedPR]

I don't get it, MedPR.

Delta L = FL0/EA; so E and A should be proportional, no?

I'm thinking that E is a constant at a given temperature. If that's not true, then I have no idea.

 

[pfaction]

Once again TPR does not go over this...or I haven't read it.
So let's pretend you're right for now. E is constant.
Stress = F/A; where A is increased, Stress is decreased.
Stress = modulus * strain; so decreased stress constant modulus must mean decreased strain.

 

[MedPR]

Once again TPR does not go over this...or I haven't read it.
So let's pretend you're right for now. E is constant.
Stress = F/A; where A is increased, Stress is decreased.
Stress = modulus * strain; so decreased stress constant modulus must mean decreased strain.

Yup.

 

[pfaction]

Just ran to my room, took a look at what TPR says about Young's. Nowhere does it say it's a constant, it says it can change depending on what stress is being applied (compression or shear).

Stress is Pressure.
Stress = Modulus * Strain
Stress and Strain are proportional <- should maybe have tipped me that E is constant.
Stress = P = F/A; Strain = dL/L0 or X/L0.
[stress]F/A = E * [strain]L/L0
increase in A causes a decrease in stress, if strain is proportional, strain decreases.

Let me ask you, is this the level of knowledge truly required for the MCAT? AAMC10 and AAMC3 didn't require this much at all.

 

[MedPR]

Still pretty sure young's modulus is a constant until you change the temperature or pass the elastic limit.

 

[pfaction]

The way you answer questions with logic and precision, I'll trust your word over TPR anyday bro.

 

[MedPR]

The way you answer questions with logic and precision, I'll trust your word over TPR anyday bro.

Well if TPR said it isn't constant, then go with that. But I think you said that they didn't mention it one way or the other. Mislki probably knows.

 

[SaintJude]

MedPr is right. Young's modulus is a constant. It is an intrinsic property of a substance. One of the few substances (if not only) that has a changing Young's modulus is an elastomer (but this = passage topic). EK and Kaplan both make it clear.

You can not change the Young's modulus of a substance by changing its area or force. And this is a favorite topic for discretes, b/c so many people start plugging in numbers for nothing.

 

[milski]

Well if TPR said it isn't constant, then go with that. But I think you said that they didn't mention it one way or the other. Mislki probably knows.

No idea. We have not mentioned anything about stress in two years of physics so far and knowing what I will have to take in the next couple of quarters, I'll be surprised if it's there. In the worst case I can see what the review books say and look it up somewhere but that's a bridge I don't have to cross yet.

 

[411309]

Seconding what medpr said. YM is determined by the material but since you are decreasing the stress you are also deceasing the strain, making YM unaffected.

 

[Temperature101]

I believe there is a question like that in TPR1 FL and I missed it because I dont remember that TBR even mention that Young's Modulus is a constant regardless you increase the cross sectional area or not...but it's good to know that now. SDN is a great source.

 

[MedPR]

Read what is in white if you want to know something about Young's Modulus. However, before you highlight, know that this information is in an AAMC test.

AAMC 11 says that young's modulus is constant for a material at a given length. In other words, until you over stretch or over strain it, modulus doesn't change