What is Soap: Definition and 103 Discussions

Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are used as thickeners, components of some lubricants, and precursors to catalysts.
When used for cleaning, soap solubilizes particles and grime, which can then be separated from the article being cleaned. In hand washing, as a surfactant, when lathered with a little water, soap kills microorganisms by disorganizing their membrane lipid bilayer and denaturing their proteins. It also emulsifies oils, enabling them to be carried away by running water.Soap is created by mixing fats and oils with a base, as opposed to detergent which is created by combining chemical compounds in a mixer.
Humans have used soap for millennia. Evidence exists of the production of soap-like materials in around 2800 BC in ancient Babylon.

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  1. C

    How does soap water membrane thickness affect surface tension?

    1.If the thickness of soap water surface decrease, whereas the concentration remain the same, how will the surface tension change? 2. If the membrane of soap water start to evaporate, its thickness become thinner and it’s concentration increase, How will the surface tension change? Thank you!
  2. abdulbadii

    Anyone very knowledgeable in making body soap?

    Is anyone very knowledgeable in making body or hand soap so can easily classify the main compounds' function and proportion Found on a body soap wrap written ingredient: Sodium Laureth Sulfate Laureth-4 Lauryl Alcohol Sodium Palmateiiii Sodium Palm Kernelate Palm Kernel Acid Paraffinum...
  3. abdulbadii

    The emulsifier inside common dish soap

    What actually typically is the emulsifier inside common dish soaps? Isn't another kind of soap, clothes or hand/body soap, also has such emulsifier in its ingredient ? But as what it seems and is found on internet, why commonly people make use of emulsifier only in the dish soap?
  4. P

    I Liquid soap pulsing as it's drawn into a syringe

    So here it is. I took a guess but I couldn't really answer, hopefully you can. Slow motion video of pulsations occurring while sucking liquid soap into a syringe.
  5. brotherbobby

    Surface Tension - Using hot soapy water to wash clothes

    I mention the details in the book (verbatim) in the form of a paragraph in green below. Later I ask my questions in blue font for better reading. "Surface tension also explains why hot, soapy water is used for washing. To wash clothing thoroughly, water must be forced through the tiny spaces...
  6. E

    Exploring Soap Bubble Oscillations: A Comparison of Force and Energy Approaches

    I have solved it with a force approach, but would like to know how to do it via an energy approach. For starters, here is the force approach. Consider a small, approximately circular, surface element of mass ##m## such that the angle from the centre to the edge of this element is ##\alpha##...
  7. mollwollfumble

    I Blowing Bubbles in Space: Can You Create a Giant Bubble in the Vacuum of Space?

    This is an experiment I would have liked to do from the ISS, but an approximation could be done in a vacuum chamber on Earth. How big a soap bubble, polymer bubble, or glass bubble could you blow in the vacuum of space? How to calculate the evaporation rate in vacuum? A liquid exposed to vacuum...
  8. Sophrosyne

    Medical Why doesn't soap or oil destroy your skin's epidermis?

    Cell membranes are made of a bilayer of amphiphilic phospholipids, where the lipophilic portions of the molecules face toward each other, and the hydrophilic portions face outwards towards the cytoplasm or the external cellular environment which is aqueous and therefore orients those...
  9. Raihan amin

    The shape of the surface of a soap film

    1. Two coaxial rings of radius R=10 cm are placed to a distance L from each other.There is a soap film connecting the two rings(that looks like a cylinder which have different radii with z coordinate. (The rings lie in xy plane)).Derive a differential equation describing the shape r(z) of the...
  10. A

    A fascinating fault with my automatic soap dispenser

    I have a Dettol automatic soap dispenser (see fig. 1) which uses a little propellor-type pump to let out a small amount of soap when you put your hand in front of the passive IR sensor. It's been working fine until just before, when I turned the lights off in the kitchen (night time, so...
  11. J

    Excess pressure inside a soap bubble

    Homework Statement Homework EquationsThe Attempt at a Solution Excess pressure inside a spherical soap bubble is 4S/R . How to deal with the cylindrical shape ? Why does the question specify it to be "long" ?
  12. K

    Surface Tension of a soap film

    I don't understand, when calculating the force to change the surface area of the film, how the length obtained in the diagram below is "l" (lowercase L). I understand that there are two surfaces to overcome, hence the factor of 2, but why is the length perpedicular to the force used and not...
  13. B

    What Force Acts Between Hemispheres of a Charged Soap Bubble?

    Homework Statement There is a total of ##Q## charge on soap bubble of radius ##R##. What force is acting on one hemisphere by the other ? Homework Equations Electrostatic pressure is ##P_e = 2\pi \sigma^2## for a spherical shell. The Attempt at a Solution ##P_e = F/A## therefore ##F =...
  14. DaveC426913

    Dish soap and water evaporation

    I want to keep a small space (oh, say, about the size of a chest humidor - call it 2 cubic feet) humid to a level of about 70% to 80%. I don't feel like using the whole humidity technology that you have to fill all the time, so I've just stuck a gallon bucket of water in there. I was wondering...
  15. EmilyBergendahl

    Interference in Thin Films: Grade 12 Optics Review

    Homework Statement Would you see the same thin film interference pattern in a film of soap surrounded by air and a film of soap on glass? Why or why not? Homework Equations None The Attempt at a Solution Yes, you would see the same thin film interference pattern in a film of soap surrounded...
  16. spareine

    Do soap bubbles reflect sound?

    Bats in my garden do not seem to notice soap bubbles. Do soap bubbles reflect sound?
  17. R

    Uncovering Wavelengths Not Reflected in a Soap Bubble Film

    1. The problem statement, all variables and given/known da A soap bubble 500 nm thick is illuminated with white light. The index of refraction of this unique soap film is 1.35 for all colors (no dispersion). a) What wavelengths are not reflected? Homework Equations 2nt=mL 2nt=m(L/2) The...
  18. Zero-shift

    How Does Surface Tension Affect Thermodynamic Potentials in Soap Bubbles?

    For a system modelling a soap bubble, the differential work done is now given by: dW = −pdV + γdA, where γ is the surface tension and A the area. Compute new differential expressions for the potentials U, H, F, G. What are the new natural variables in each case? Are there any new Maxwell...
  19. T

    Light wave incident on and passing through a thin soap film

    here is the problem. i got 0.5 from the fact that thickness = (m)(lambda)/(2nf) other equation for thickness is thickness = (m+1/2)(lambda)/(2nf)
  20. Derek Francis

    Double Edge Wet Shaving - My Gear & Experience

    A current hobby of mine. Long term savings in that a DE blade costs 10-30 cents compared to $1-4 disposable razors/cartridges. An initial purchase of a razor and brush together would cost no more than $40 on Amazon and they last a lifetime. I've tried electric razors ; anything under $150...
  21. T

    Pressure inside a soap bubble just under surface

    Homework Statement What should be the pressure inside a small air bubble of 0.1,, radius,situated just below the surface? st of water=7.2 *10-2 and atmospheric pressure=1.013*105. Homework EquationsThe Attempt at a Solution I am of the understanding that the pressure inside the...
  22. H

    Fluid - Work done to blow a soap bubble

    Hi everybody, I now encounter some problems when try to solve this: Problem statement: Calculate the work done to blow a soap bubble to radius R. Knowing that the process is isotherm, the atmospheric pressure is H, the surface tension is γ. Solution: $$A = A_{1}+A_{2}$$ In which A1 is the work...
  23. S

    Capillary action at different temperatures

    Hi guys, I'm doing a project at the moment revolving around capillary action and surface tension. Today I conducted an experiment to observe capillary action in a capillary tube and paper towel at different temperatures of water. I don't understand why I've got the following results: As you...
  24. F

    Soap and water not suitable for washing paint thinner off?

    I found paint thinner (aka. mineral spirits in US, white spirit in UK) very useful in cleaning tough stains on tiles, etc. However I notice that even after washing my hand several times and rubbing for a long time with soap the smell of the paint thinner does not go away from my hands. I'm a...
  25. H

    How Does Weight Affect Speed of a Soap Box Car?

    Homework Statement I was wondering about how the placement of weight affects Soap Box Cars. I have been racing them for 5 years now, and I cannot find any information. I was wondering if there was a formula to find the relationship between speed and weight, and how to solve it. For instance, if...
  26. S

    Sound Generation: From Soap Bubbles to Nukes

    A soap bubble or a nuclear detonation emit a sound created by the sudden release of pressured air? Am I correct? How is the sound of a knock on the door, two billiard balls hitting each other, etc. How is the sound generated in their cases? Thank you.
  27. Greg Bernhardt

    Milk Food Coloring And Dish Soap Experiment

    This is a fun, easy and super kid friendly experiment. Now, what exactly is happening here? :) https://www.youtube.com/watch?v=rqQSlEViNpk
  28. N

    DIY Cream Dispenser: How to Build a Handheld Squeezer with Your Daughter

    Hi everyone, Just new to the forum and a novice electronic geek. I am trying to build a small cream dispenser with my daughter. Basically a hand held device that when you press a button automatically squeezes the bottle and dispenses a preset amount of cream. I know there are probably...
  29. O

    Why Does Pepper Move to the Edge of the Plate in the Soap Experiment?

    Hello. I have a question... I think that you know the experiment with pepper and soap. (you put water on plate, than you put a lot of pepper on in, than you put on your finger some soap and than you touch the plate). The pepper goes to edge of the plate. Only some of them fall in the water. It...
  30. R

    Steel Soap bars: magnetic core, solid?

    I bought a Stainless Steel soap bar and it works, it just does. It was from China and hollow inside and I would like to know if that's either a cost cutting measure or how the bar works? What would happen if it were solid? Another thing would be if it had a magnetic core, or made from a metal...
  31. U

    Soap bubbles sticking to each other

    Homework Statement Two soap bubbles of radii 3cm and 2cm come in contact and sticks to each other. Calculate the radius of curvature of common surface. The Attempt at a Solution Excess pressure inside soap bubble = 4T/R Let the radius of common surface be R' \dfrac{4T}{R'} = \dfrac{4T}{r_1}...
  32. M

    Soap film analogy and sand heap analogy

    Guys, do you know any comprehensive website or reference that explains everything about soap film analogy and sand heap analogy? Including their concepts, procedure on how to perform them and some animations. It will be more useful if the discussion also deals with the reinforced concrete...
  33. S

    How Do Soap Bubbles Display Vivid Colors Through Light Interference?

    on a soap bubble colours can be seen.my textbook says its due to the interference betwewn light waves from the top and the bottom surfaces of thin films.but how?so confused:confused: i tried googling for answer but still i can't find it
  34. Greg Bernhardt

    FDA puts antibacterial hand soap to the test

    FDA examining antibacterial soaps, body washes http://www.cnn.com/2013/12/16/health/fda-antibacterial/
  35. J

    Soap Box car - heavier better ? Part II

    After reading throught the original thread about soapbox cars, I have a better understanding of what is happening. The soapbox derby that I'm in has few rules. You must have a 6" or less wheel, steering and some sort of brake. The hill is a constant slope and there is a 10' push zone. From...
  36. andyrk

    Soap Film Formation: Explaining the Phenomenon

    When we dip a wire ring in a soap solution and then take it out, why does it form a soap film inside? Is there any explanation behind it?
  37. Saitama

    Surface tension - thread in soap solution

    Homework Statement (Ans: ##\pi F/(2L)##) Homework Equations The Attempt at a Solution I am not too much familiar with these type of questions so I don't really how to begin with this. Also, I don't understand the question here. Do we have to consider it in the vertical or...
  38. K

    Discover the Magic of Soap Making: Experiment with Different Solutions at Home

    I want to start a home project to creating different soap solutions. Dish washing detergent, carpet cleaning solution, and car cleaning soap are my main focuses. I have no idea where to start as my internet research is getting no where. What is soap made of and how can I experiment with...
  39. M

    Can a metal ring and soap solution create expanding bubbles?

    I've heard that, when a soap bubble is given a charge, it expands. I was just wandering whether, when you wet a ring made of metal with a soap solution and blow to it slowly, the bubble created expands because of theat above principle. Does The friction between the metal ring and the bubble...
  40. C

    How does a Soap dispenser work

    Homework Statement My soap dispenser does not work, but when i block the pump end the soap comes out, can someone explain to me why? Homework Equations I am looking for a relevant equation to prove why it doesn't work The Attempt at a Solution
  41. L

    Caffeine Soap; does it really work?

    Evening all, I've been curious about these caffeine soaps lately and thought that this would be the place to discuss about it. My almost-favorite website United Nuclear claims: "As it turns out, our good old friend Caffeine reaches the bloodstream faster through skin absorption...
  42. T

    How can a soap film be stable?

    It is said that a soap film will find the surface with the minimum area. If the two interfaces between the soap and the air meet, the soap film can effectively reduce its area by bursting. You would think that if you simply hold a soap film up vertically, all the liquid would want to go to the...
  43. P

    What is the formula for the charge of a charged soap bubble?

    Homework Statement A soap bubble of radius 0.1mm has a wall thickness of 3.3x10^-8m, and is charged to a potential of 100V. Give a formula for the charge of the bubble. I know this is probably a really easy question, but I've only ever done problems with spheres of negligible wall...
  44. A

    Acid-Base Titrations and Liquid Soap

    I am doing an acid-base titration on liquid soap. I understand that buffers are used in soap. Would that affect the results of my titration? If so, how would I overcome this? Arthur.
  45. G

    Extracting Sodium Hydroxide from Soap: A Step-by-Step Guide

    is it possible to extract sodium hydroxide from liquid soap? i need to test the sodium hydroxide. if it is possible, how would i do it?
  46. G

    Testing amount of sodium hydroxide in soap

    i'm doing a task to find the amount of sodium hydroxide (NaOH) in a liquid soap. i have to use titration in it. how exactly would I do this? thanks
  47. T

    Washing machine motor soap extruder

    Hello I am trying to start a small home business making soap. I am on a really tight budget and also very new to the extrusion process. While I may be extruding soap, I understand that the process is very similar to plastic extrusion. I want to extrude soap bars using a machine...
  48. Q

    Two soap bubbles coalesce, what is the surface tension?

    Homework Statement Two soap bubbles of equal radius 'r' coalesce isothermally to form a bigger bubble of radius 'R'. If the atmospheric pressure is P0, find the surface tension of the soap solution. Homework Equations Surface energy = surface tension x increase in area (W = T.ΔA)...
  49. V

    Radius of Curvature at Soap Bubble Contact Point

    Two soap bubbles of radius r and R are in touch find the radius of curvature of their point of contact? (Both bubbles are touching each other with their external surfaces) I have no idea about this question. can you please try to help>