7 Simple Questions That Scientists Still Can't Answer

6. Why Is Ice Slippery?

Seems pretty obvious, right? Ice is slippery because ... well ... because it's ice. It was thought until pretty recently that the slipperiness of ice was due to the pressure of your foot/skate/whatever was causing the top layer to melt. It sounds like a pretty convincing solution, but when somebody crunched the numbers, it just didn't check out. True, pressure will cause ice to melt, but in reality, even an above average-weighted person would not be able to exert enough pressure through a skate to make this happen. This led scientists to believe that perhaps it was the friction of the skate moving across the ice that caused it to melt. Unfortunately, this doesn't check out either, as ice is still slippery when you're stood still (although, granted, you are less likely to fall over because you're stood still). So with these two options ruled out, the solutions starts to get distinctly weirder. The best guess we have at the moment is that the layer that forms on top of the ice is not a liquid, but a "supersolid skin". With this skin, the bonds between the water molecules are stretched, but they remain unbroken (unlike in a liquid). It is the elongation of these bonds that supposedly generates an electrostatic field that causes the slipperiness by sort of "levitating" you off it. Others, however, remain unconvinced, but they all agree that this is way more complicated than it has any right to be.