# Design experiment to determine bending strength and torsion of ruler

1. Jul 23, 2013

### patehi

hello everyone!

so as the title suggest, i wonder if anyone would have any idea to design a simple experiment to determine the bending strength and torsion of a plastic ruler.
it doesnt need to be extensive, as the value of the strenght itself isnt important. i just wanna know e.g how far could the ruler bend before breaking. and when i have the result, i could compare it with another plastic ruler.

I dont have any measuring devide, all i have is a protractor and ill have some way of determining the angle of bend.
(i also have a dynamometer if that would help in any way)

here is my suggestion of the bending strength experiment:
[Broken]
http://imageshack.us/a/img199/3729/vj0e.png [Broken]
for this experiment i jsut put the ruler on the table and apply F at the end and determine the angle. Although it is actually pretty inaccurate to read the angle to determine its strengh :/

and here another suggestion:
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http://imageshack.us/photo/my-images/9/rjkx.jpg/

i put the ruler on 2 objets and apply F to the middle part.ill determine how far will it bend in cm.

Do you guys have any suggestion for this experiment? as i said, i have limited device and i would prefer an experiment as simple as possible.

Also, i would be needing a design experiment to determine the torsion of the plastic ruler too. Alhthough i dont really know how to do it without proper measuring devide :/

So i would appreciate if anyone could give an idea about it! Thank you!

Last edited by a moderator: May 6, 2017
2. Jul 23, 2013

### PhanthomJay

I am not sure what you are trying to accomplish. If you are placing a force on the ruler less than that required to break it, and determining its deflection or rotation angle under that force, you will determine how stiff the ruler is and not how strong it is. For example, certain grades of aluminum have the same strength of certain grades of steel, but the aluminum of the same dimensions as the steel will deflect three times more under the same load. Or you can take a low strength steel and a high strength steel and discover they will have the same deflection under the same load up to the yielding failure of the former.