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Question: Why is ice slippery?
When two objects rub against each other, the molecules at the surfaces interact. The nature of the interaction will determine how easily the two surfaces can slip by each other. The amount of slipperiness depends on the attraction between the molecules, and how they are arranged. You have to push to get any object to move across any surface. We call the force that it takes to get one surface moving over another the force of friction.
If the surfaces are very smooth, you won't have to push very hard to get them moving. If at least one of the surfaces is rough, like sandpaper, it will take much more effort. Overcoming the force of friction also produces heat. You can feel this if you rub your hands together quickly over and over again. I often do this to warm my hands during the winter.
Ice is made of water molecules, which are very small as molecules go. They are the smallest molecules that can form a solid at temperatures we find on Earth. This makes for a very smooth, and slippery, surfaces when water freezes to make ice. If you wear skates, the friction from the skate will cause enough heat to melt the surface of the ice, making it even more slippery. This reduces the force of friction you need to overcome to get things moving.
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