From It’s ok to be Smart:
I’m guessing you’re pretty familiar with ice. We use it in our drinks, slip on it, skate on it, worry about climate change melting it. But have you ever stopped to really think about this stuff? The freezing and melting of water affects so much of our world. It’s ice crystals in thunderclouds that create lightning. Ice is powerful enough crack boulders, float stones, and alter entire landscapes. Ice is such a common substance, you’d think we’d know everything about it by now. But it has some secrets and weird properties we’ve only just begun to figure out. One question about ice that’s, still not totally answered, is one of the most obvious: why is ice slippery? It’s a more complicated answer than it seems!