Tribology - Hand Washing

Ummmmm can't say that I've noticed this before Jules....

Maybe I should spend longer in the washroom eh?

John

Or don't leave before your hands are dry?

Water is slicker than skin. Hands slide easily when wet.

Skin is sticky. Hands stick when clean and dry.

Oil is slicker than water. Perhaps you not only sweat a lot but sweat very quickly. Soon as the hands become oily, oily skin is slicker than slicky water wet or sticky clean hands. On second thought, perhaps germs jump out of the contaminated air dryer and run around really fast enough to make the creepy skin slipperly slick. Those air dryers recycle contaminated air and remit some of the most contaminated air humans contact.

How can they emit some of the most contaminated air humans contact??

They take air in from the room where you are standing breathing the stuff in and out... I bet the heater kills off some of the bugs in the air, so the outlet jet of air would be cleaner than in the room...

I think I'd rather breathe the air from a hand drier than, say, from a sewer!!

John.

True! Use a paper towel.

I think it might be the case that as the 'guest' said that with water acting as a lubricant, maybe with traces of soap? would provide a slippery start and as the water evaporates the clean, dry skin increases the friction rapidly, but then as the hot air makes the pores regenerate some skin oils the end result would be less friction...

Or maybe its a psychological response to ease off the pressure between the hands when they feel dry so reducing the friction?

Well, the water does create a fluid film that allows the skin of one hand to become nearly intimate with that of the other hand while separated by a thin, lubricating film of water.

After evapouration, its just skin against skin. One would think that the oils normally present on the surface of the skin have been washed away, and the skin temporarily takes on a characteristic similar to clean rubber. That's fine with me, as the purpose of washing my hands is to make them clean!

And, I dislike the forced-air dryers, as they are perhaps more efficient than chopping trees into paper towels, but I prefer a paper towel. It's hard to wipe your face and glasses with a forced-air dryer! Are they less sanitary? I would not think so, as the air used is blown over a heating element that of course does not kill all bacteria and viruses that are present in moving air, but it has to kill some of them.

Now, if someone would market a forced-air dryer that uses sufficient UV light radiation to purify the air before it is blown over the heating element, then one has the 100% germ- and virus-free hot air supply. And, due to the cost of such a unit, the decision may be in favour of paper towels. Ah, I sense a plot forming, and maybe this is my way to return paper towels to the washroom. Viva la Revolution!

Ing. Robert Forbus

As for cutting down trees for paper towels, we buy towels that are made from 100% recycled paper products.

Our company just replaced half of our paper towel dispensers with high efficiency blowers. These blowers are so loud that you cannot be heard if you talk loudly anywhere in the restroom, and it is not a small restroom.

Which is the most environmentally detrimental or costly; producing a paper product or producing electricity to run this noisy hand drier???

I also miss the opportunity to keep the towel in hand to exit the restroom using it to protect from contact with the door handle where a multitude of bacteria reside.

It is my observation that most people, myself included, only use part of drying cycle and complete drying hand on pant legs.

I think that Electroman is probably right. Although I have dry skin, i.e not noticably sweaty or oily, the heat does probably bring skin oils to the surface. End of topic unless there are any blinding insights from anyone else - Thanks.

I also agree that paper towels are better. How many trees are cut down, now or during the carboniferous era, to run the power stations to provide the electricity to feed the distribution system to convert into rotary motion and resistive heat to save the cost of making a sustainable grown harvested tree, or as is usual, recycled paper for a paper towel - sorry folks off on one!

Lubrication of the hands is true when it is only hand to hand. I have been in situations where my hands were very dry, also calloused. I was not able to lift a fairly heavy cardboard box with the dry hands, they were very slippery. After moistening the hands it provided a far better holding (traction) capability and I was able to lift the box with ease. I think the water on my hands actually penetrated the cardboard - softening it, thus it was easier to hold. Any ideas on this???

Water forms a strong cohesive/adhesive in thin layers, easily shears in thicker layers.

Thanks. I guess that for the different states, we have:

a) hands wet, lot of water, shear = Low friction

b) almost dry, just a few water molecules, hang together - friction increases.

c) Dry, no water, smooth clean skin, = Low friction

Voila!

the reason why you find you hands moving smoothly when it dries is due to lower coeff of friction of hot air after the hand has dried off.

Thanks, fits in with my post #13