- #1
arhzz
- 284
- 58
- Homework Statement
- Determine the surface tension γ of a liquid with the help of the capillary effect. The capillary has an inner diameter of 0.5 mm and the liquid with a density of 875 kg / m3 rises 3.4 cm. To do this, derive the formula for γ from the equilibrium of forces
- Relevant Equations
- F = mg
Hello! To this I did what was recommended and this is what it looks like
$$ F = mg $$
$$ F = \rho * V * g $$
$$ F = \ rho * \pi^2 * h * g $$
Than for the surface tension I did the same thing to get an expression for F.
$$ y = \frac {F} {2 \pi r}$$
Than tried to get F out and than equate both of the equations, than F and pi would be on both sides so it would cancel out leaving me with this.
$$ \rho * r^2 *h * g = 2 * y * r $$
Than I tried to get the tension out so I moved everything accordingly and got this $$ y = \frac {h* \rho*g*r} {2}$$
The result should be 0,0365 N/m
Now the reason why I am posting this question is why is it recommened to use the equilibrium of forces? I tried to calculate the tension, with an equation that was given to us in class, it doenst include any forces and I got a whole diffrent result. I'd assume this is the right way to do it given the suggestion in the task itself but why? And in a situation where this "hint" wasnt given to me I'd never come to use this variant, id just do with the formula provided in class. Any insights?
Thank you!
$$ F = mg $$
$$ F = \rho * V * g $$
$$ F = \ rho * \pi^2 * h * g $$
Than for the surface tension I did the same thing to get an expression for F.
$$ y = \frac {F} {2 \pi r}$$
Than tried to get F out and than equate both of the equations, than F and pi would be on both sides so it would cancel out leaving me with this.
$$ \rho * r^2 *h * g = 2 * y * r $$
Than I tried to get the tension out so I moved everything accordingly and got this $$ y = \frac {h* \rho*g*r} {2}$$
The result should be 0,0365 N/m
Now the reason why I am posting this question is why is it recommened to use the equilibrium of forces? I tried to calculate the tension, with an equation that was given to us in class, it doenst include any forces and I got a whole diffrent result. I'd assume this is the right way to do it given the suggestion in the task itself but why? And in a situation where this "hint" wasnt given to me I'd never come to use this variant, id just do with the formula provided in class. Any insights?
Thank you!