# Quick Question # Stress+Strain

Discussion in 'Physics' started by Ben_C, Mar 10, 2011.

1. ### Ben_C Thread Starter Active Member

Oct 19, 2010
65
4
When working out the stress in a wire or bar do we need to take the length into concideration? Stress = F/A.

I have read that its just the cross sectional area that is needed but surely thinking about it logically we would have to work out the whole area of the material? Doing this by including the length :S

I have a question that asks me to work out the stress..
A wire is 2.5mm in diameter and 2m long, with a force of 12N applied and it stretches 0.3mm.

Now do I just do
Pi x 1.25^2
or
Pi x 1.25^2 x l
to work out the area....

2. ### BillO Distinguished Member

Nov 24, 2008
985
136
A hint...

Strain is the material's response to stress. The stress is given in this case, however, you have not mentioned the nature of the stress.

I can imply from what you said that you are talking about tensile stress Yes/no?). If indeed the strain is also given (.3mm) and the length and diameter of the material, then the only thing left to calculate would be the Young's modulus.

Look up the equation for response to tensile stress here: http://en.wikipedia.org/wiki/Young's_modulus

See if length is a "concideration" in ny part of the discussion.