# Calculating compressive force

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#1
A steel bar of length 40mm and cross-sectional area 4.5x10-4 m^2 is places in a vice and compressed by 0.2mm when the vice is tighted. Calculate the compressive force exerted on the bar.

I know the formula is CS = F / A

I'm not given the Force. So how do I work it out?
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1 year ago
#2
You should use the formula for Young's Modulus:

where is the stress and is the strain. In this situation, the stress might be referred to as compressive stress since stress usually refers to stretching, but since we want the compressive force anyway we don't have to worry about the sign (i.e. would normally be negative in this situation, but we want the force in the same direction so it doesn't matter).

This gives:

Re-arranging, you can get an expression for F:

Then, substituting values (Young's Modulus of steel is around 200 GPa):

Which gives a final force of , or .
1
#3
(Original post by GgbroTG)
You should use the formula for Young's Modulus:

where is the stress and is the strain. In this situation, the stress might be referred to as compressive stress since stress usually refers to stretching, but since we want the compressive force anyway we don't have to worry about the sign (i.e. would normally be negative in this situation, but we want the force in the same direction so it doesn't matter).

This gives:

Re-arranging, you can get an expression for F:

Then, substituting values (Young's Modulus of steel is around 200 GPa):

Which gives a final force of , or .
Thank you so much for you detailed answer, I've worked it out now.
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