- #1
FaraDazed
- 347
- 2
Homework Statement
A needle can be supported by the suface tension of water.
Given the density of steel (7900kg/m^3) a needle with diameter 0.25mm, the surface tension of water (0.072 N/m) and acceleration due to gravity (9.8) show that this is reasonable.
What is the largest diameter needle that could be supported by the surface tension.
Homework Equations
[tex]
\gamma=\frac{F}{L} \\
\gamma L = mg \\
2 \gamma l = mg
[/tex]
That last equation is for the largest possible mass
The Attempt at a Solution
So far I have done.
[tex]
\gamma L = mg \\
0.072 × 2.5 × 10^{-4} = 9.8m \\
1.8×10^{-5}=9.8m
[/tex]
But if I carry that through I get some crazy huge number for the mass which cannot be correct. I suspect that L is not the diameter of the needle but the true length but without that given I don't know how to find it. I know what to do or rather how to use all the values given apart from the density of steel so maybe that is relevant to my first issue but not sure how.