- #1
hcho88
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Homework Statement
First part of the question was "Why is it possible to float a wax-coated stainless steel needle on the surface of water?" and I've already answered that, but I'm having trouble with the second part of the question, which is:
If the surface tension at the interface is 0.073 N/m and the density of the steel needle is 7.8x10^3 kg/m^3, what is the maximum diameter of a needle that can float this way? (Hint: start by finding the weight of the needle. You may assume that the needle is cylindrical in cross-section)
Homework Equations
Density = mass / volume
h = (2[tex]\sigma[/tex]cos[tex]\Psi[/tex]) / ([tex]\rho[/tex]g[tex]\alpha[/tex])
V of needle = width x (2[tex]\Pi[/tex]r^2)
I'm actually not too sure which equations I need...
The Attempt at a Solution
[tex]\sigma[/tex] = 0.073N/m
[tex]\rho[/tex] of stainless steel needle = 7.8x10^3 kg/m^3
Well it says to start by finding the weight of the needle, and I wasn't sure how to approach that in the first place, so I wasn't able to make a start.