MadSci Network: Physics |
Clothes stick to wet skin because:
The droplets of water on your skin flatten out between the fabric and your skin, partly because of the weight of the fabric and partly because of the surface tension of the water. This means that the droplets can minimise their contact with air (and hence their overall surface energy) by spreading out into a pancake between the two surfaces. Any relative velocity between the fabric and the skin will then create a velocity gradient in the flattened water droplets, which creates a force opposing the velocity. The property of the water (or any fluid) that does this is known as viscosity. The more viscous the fluid, the higher the opposing force will be. The result is that it is difficult to pull clothes over wet skin. In the case of dry skin, air also has viscosity but the effect in this case is tiny for two reasons. Firstly, the viscosity of air is about a hundred times smaller than that of water. Secondly, air does not have surface tension and so the gap between your skin and the fabric is much larger, decreasing the effect of the already small viscosity.
Cheers,
Graeme
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