Algodoo

Simulates a drop of water on skin. (Simplified) watermolecules collide and create a velocity/momentum distribution (Maxwell-Boltzmann-Distribution). Usually molecules attract each other and form a drop of water, but sometimes a molecule gains enough momentum to leave the attracting forces and leave the drop, taking kinetic energy with it. Therefore the remaining molecules have a smaller average momentum and the drop as a whole has a lower temperature. Since it is in contact with the skin it gets heated up as long as it takes to completely evaporate. The skin cooles down in the process (indicated by the color change).