I I found 2 formulas about surface tension -- which one is correct?

AI Thread Summary
The discussion centers on two formulas for calculating surface tension, specifically for a solid disk and a thin ring. The formula for the disk is given as γ_disk = W/C, while for the ring it is γ_ring = W/2C, highlighting the difference in interface lengths. The reasoning behind this difference is explained through the analogy of surface tension as a distribution of tiny parallel springs, where the ring has a longer interface, necessitating a lower spring constant to support the same weight. The choice of formula depends on the specific scenario being analyzed. Understanding these derivations is crucial for applying the correct formula in practical situations.
samy4408
Messages
62
Reaction score
9
1666779837352.png

1666779865756.png
 
Physics news on Phys.org
Can you provide the context or references of how these formulas were derived?
 
kuruman said:
Can you provide the context or references of how these formulas were derived?
I found the first one by typing surface tension formula on google , and the second :
1666789001608.png
 
Which you use depends on what question you wish to answer. Say you have a solid disk and a very thin ring both of circumference ##C## and weight ##W## floating in a fluid. In the case of the disk, ##\gamma_{\text{disk}}=\dfrac{W}{C}##; in the case of the ring, ##\gamma_{\text{ring}}=\dfrac{W}{2C}.##

You can imagine the surface tension force as the resultant of a uniform distribution of tiny parallel springs around the length of the interface of the object and the fluid with ##\gamma## playing the role of the spring constant. The ring has twice as long an interface (on the inside and outside) as the disk and therefore twice as many springs. Thus, half the spring constant is required to support the same weight.
 
Thread 'Gauss' law seems to imply instantaneous electric field'
Imagine a charged sphere at the origin connected through an open switch to a vertical grounded wire. We wish to find an expression for the horizontal component of the electric field at a distance ##\mathbf{r}## from the sphere as it discharges. By using the Lorenz gauge condition: $$\nabla \cdot \mathbf{A} + \frac{1}{c^2}\frac{\partial \phi}{\partial t}=0\tag{1}$$ we find the following retarded solutions to the Maxwell equations If we assume that...
I passed a motorcycle on the highway going the opposite direction. I know I was doing 125/km/h. I estimated that the frequency of his motor dropped by an entire octave, so that's a doubling of the wavelength. My intuition is telling me that's extremely unlikely. I can't actually calculate how fast he was going with just that information, can I? It seems to me, I have to know the absolute frequency of one of those tones, either shifted up or down or unshifted, yes? I tried to mimic the...
Back
Top