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Simple question about young's modulus

by lionely
Tags: modulus, simple, young
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lionely
#1
Nov28-12, 08:59 PM
P: 523
I did a practical worked the gradient and calculated E, of a wooden metre rule.

What I want is a value to compare my value with, I got 5 N/m2

So 5N will bend the ruler 1m? Seems likely right?
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Simon Bridge
#2
Nov28-12, 09:09 PM
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So 5N will bend the ruler 1m? Seems likely right?
Well - presumably you'd reach the elastic limit of the ruler before then.
Though your argument does not seem to match the units...

Compare:
http://www.madsci.org/posts/archives...3677.Ph.r.html
... and read the discussion: particularly about accuracy.
lionely
#3
Nov28-12, 09:10 PM
P: 523
On that page isn't that Mega Pascals?? I got 5Pa

lionely
#4
Nov28-12, 09:12 PM
P: 523
Simple question about young's modulus

and maybe on that page those are MUCH higher maybe cause they calculated it using woods of greater thickness,length, etc.
lionely
#5
Nov28-12, 09:18 PM
P: 523
Ohhhh LOL i'm sorry I didn't even see what I typed
my mind was away. I didn't mean 5 newtons would bend it 1m
Simon Bridge
#6
Nov29-12, 01:35 AM
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Would you get a higher modulus if you used a thicker beam?
It's a material property. How is the modulus defined?

You can also look for other people who've done the same and talked about it.
It's a common enough experiment - done either by vertical deflection by weights or by Timing harmonic motion.
lionely
#7
Nov29-12, 04:17 PM
P: 523
I found out my value is very wrong D: I need to recheck my calculations
lionely
#8
Nov29-12, 04:35 PM
P: 523
I am so stupid =.= I left off a 10^-8 somewhere in my calculations.

New value which makes sense NOW is 5.10 x 10^7Pa.
lionely
#9
Nov29-12, 04:43 PM
P: 523
Sigh again i was wrong I did it over again I got 5,108.1 MPa
Simon Bridge
#10
Nov29-12, 09:32 PM
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When you have measurements on such a wide variation of scales, it is very easy to misplace lots of zeros :)

You can see from the discussion of accuracy in the article that these can get very big (as much as 56% it says) so you only need the right order of magnitude. "Conclude: Youngs modulus for a wooded meter-rule was experimentally determined to be _____GPa. This agrees to the same order of magnitude as an accepted value of _____GPa given in ref. ______."

If you did errors then you can also comment on how good the agreement was.
lionely
#11
Nov30-12, 05:41 PM
P: 523
Thank you.


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