text: while boiling water water why water does flow out but milk does?   i agree with kunche and i'm expanding his explanation that's it.  milk is highly viscous fliud. so it will always have a dry film on the top of it due to exposure to atmosphere. this dry film will not allow gases or water vapur which come out when heated to escape out. so like a baloon the milk layer expands and rises high. when you disturb that top layer by sprinkling water or blowing air when it is expanding you will see a lot of gases escaping out as though some work has been alloted to them. that is the proof that gases are trapped inside that layer. but coming to water it has very less viscosity. the particles or molecules will move aside freely to allow the water vapour to escape out. that's why there will not be any rise in the layer. that's the very reason why you see more vapuors coming out of water compared to milk. lol dan. that's really good one. i couldn't help laughing out in my cabin here. but let the kids learn. don't discourage them. this questions and answers are the proof for technology helping kids learn fast and getting answers all round the world. bye.