Calculating the surface tension using the method of Lecomt de Nouy

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SUMMARY

The discussion centers on calculating surface tension using the Lecomte de Nouy ring method. The user initially misapplied the formula, leading to an incorrect surface tension value of 0.22 N/m instead of the correct 0.1016 N/m. The key error was in misunderstanding the force calculation, where the weight of the ring (mg) needed to be included. After clarification, the user successfully recalculated the surface tension using the correct interpretation of the formula.

PREREQUISITES
  • Understanding of surface tension concepts
  • Familiarity with the Lecomte de Nouy ring method
  • Basic knowledge of force and weight calculations
  • Proficiency in using the formula y = F / (4πr)
NEXT STEPS
  • Study the derivation and application of the Lecomte de Nouy ring method
  • Learn about the relationship between force, mass, and weight in physics
  • Explore common mistakes in surface tension calculations
  • Investigate the effects of temperature on surface tension measurements
USEFUL FOR

Chemists, physics students, and laboratory technicians involved in surface tension experiments and measurements will benefit from this discussion.

arhzz
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Homework Statement
The surface tension can be determined using the Lecomte De Noüy ring method. The mass of the ring is m = 4.9 g and the diameter d = 64.1 mm. The tensile force just before tearing is in water at 25 ° C is F = 0,089 N. Calculate the surface tention
Relevant Equations
y = F/4*pi*r
Hello! I am having unexpected difficulties with this problem.A friend showed me an article regarding the Lecomde ring method,and at the bottom was this little problem that to solve.I've done it like this.

$$ y = \frac{F}{4\pi r} $$ where F is the given force and r is = 0,0325 in meters. The value I get is y = 0,22 N/m. But according to the solutions this is wrong,the right solution should be y = 0,1016 N/m.I highly doubt they are wrong,which means I made a mistake somewhere but I don't see where.The only formula that appered in the article was this and the usual surface tension.What am I i missing here.Thank you!
 
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You are given the mass of the ring. Does the force you are given include the weight of the ring?
 
arhzz said:
Homework Statement:: The surface tension can be determined using the Lecomte De Noüy ring method. The mass of the ring is m = 4.9 g and the diameter d = 64.1 mm. The tensile force just before tearing is in water at 25 ° C is F = 0,089 N. Calculate the surface tention
Relevant Equations:: y = F/4*pi*r

What am I i missing here.
You are misinterpreting the formula. The one here gives the expected answer and explains how the terms are put together.
 
Last edited:
Okay so I've tried using the formula where the mass of the ring is take into account.

$$ F = m + 4
\pi * r * y $$

If I try to get y out of this it should look like this; $$ y =
\frac{F-m}{4
\pi r} $$

But I still do not get the wanted result.
 
The weight is ##mg## not ##m##.
 
kuruman said:
The weight is ##mg## not ##m##.
Ohh,it said wait not mass,my bad I didnt read carefully.Now I get the right result,sorry for the silly mistake and thank you for your help!
 
The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?

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