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(simple Q) Cutting yourself with substances on your skin.

  1. Feb 2, 2007 #1
    I am looking for an explanation about a simple physic phenomen.

    When washing plates and ustensils, I would manipulate knives and, from times to times, would cut myself a bit. Does it matter if your hands are wet or dry and what does the water do on the surface of the skin that can influence the blade to make or not an incision in your skin.

    My remark is that water soften your skin and makes it more fragile therefore it should be easyer to cut it. My hypothesis is that by making it soft, the water protects the skin by filling holes and makes the skin more difficult to be cut since the water molecules will have a tendency to deflect the blade. What's the real explanation of that daily experience ? What changes with other substances ? Which makes it easyer or thougher to cut ?

    P.S: Sorry if this is posted on the wrong forum
  2. jcsd
  3. Feb 2, 2007 #2
    What makes you think that water molecules will deflect the blade?
  4. Feb 4, 2007 #3
    something that is more dense will generaly be harder to cut(i think), but if the water reduces the structure in our skin, then it might make it easier. like diamonds are very dense with C, but also have a very strong structure.
  5. Feb 12, 2007 #4
    The surface of our skin is composed of 15 to 30 layers of Keratinized cells. Basically a layer of dead cells filled with keratin. The maintenance of this layer depends on oils secreted from the sebaceous gland. When you are washing dishes you are using an emulsifier (soap) which washes away the oil on your skin. Another Factor to consider is that skin is water resistant, not water proof. So when you immerse your skin in fresh water, eventually osmotic forces may cause water to move into the epidermis(skin), which makes the cells get inflated like ballons. Since the cells are swollen, the membranes of the cells are not as flexible and are more likely to burst if pressure is applied to the membrane. So I am assuming skin is more susceptible to mechanical damage (cuts by knives) when immersed in water. When you add soap into the picture, I think skin would be even more susceptible to mechanical damage, since your washing off the oils, which maintain the skin cells.
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