Why does shaving foam stop the mirror from steaming up?
Question
Hello Guys,
Very good job! I whole heartedly approve of making science approachable for non-scientsists. You guys manage to do this very well.
When I take a shower the mirror in the bathroom mists up. This is clearly a process of condensation of warm moisture from the shower, condensing on the cool surface of the glass of the mirror. If one wipes the mirror, with say a towel, then the condensation returns relatively rapidly. However, I have noticed that if I rub a small amount of shaving foam onto the mirror surface, then the condensation is removed and no further condensation is formed on the mirror. I would like to know what is happening to cause this effect? Is it something along the lines of a wet t-shirt becoming translucent when wet? Why does the foam get rid of the moisture and how does it prevent further condensation from occurring? Kind regards
Brett
Answer
Dave - In some senses, it doesn't actually stop it steaming up. Steam is lots of little droplets of water. When the light hits it, the light gets bent and so you get a very distorted image which, when you move away from it, just looks like a kind of mist. What the shaving foam does: there are lots of detergents in it and those detergents reduce the surface tension of the film of water so it doesn't form lots of little droplets. It just forms a big flat sheet that you can see through much better, so you can see through it even though the water is still condensing.
Ben - So there's literally the same amount of water there; it's just a change in the structure of the water. So why do the droplets make it so hard to see things?
Dave - Because water has quite a high refractive index - when light hits it, it bends. If it hits this curved surface of a droplet, each one basically acts as a little tiny lens, light is bounced off in all sorts of different directions and makes it looks essentially white. This breaks up the image and makes it look misty.
Ben - Fantastic! Well very interesting. Not perhaps what you're supposed to use shaving foam for but if it works, it works.
Comments
I've been wondering for so
I've been wondering for so long until i read this.Thank you very much.The only thing else i can say it is a little hard to understand for kids who might read this.I know this as i am a kid myself.
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