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t’s a moonless night. The wind howls outside. A door opens slowly, as if pushed by an invisible hand.

“Cre-e-e-a-k.”

That sound — a horror movie cliché — is the result of friction. A stealthier entrance calls for oiling the door’s hinges.

Friction is everywhere — from a violinist bowing a string to children skidding down a slide. In the right situation, the ubiquitous force can have big effects: Interleave the pages of two phone books, and the friction between the pages will hold the books together so tightly that they become strong enough to suspend a car above the ground.

But scientists can’t fully explain, at the scale of atoms and molecules, why one pair of materials sticks while another moves with ease. The extreme slipperiness of ice, for example, has been a puzzle for more than 160 years. The multitude of water molecules on an icy surface creates a sheen that can send a car spinning or a penguin tobogganing. But getting a handle on the details of how this slippery surface arises from the water molecules is surprisingly tricky.

Despite its everyday nature, “we still don’t really understand a lot of things about friction,” says mechanical engineer Ali Erdemir of Argonne National Laboratory in Lemont, Ill. On its most basic level, friction results from the interactions between atoms in two materials that are butted up against one another. But, Erdemir says, “there is a disconnect” between the large-scale processes of friction that we can see, feel or hear and the smaller, atomic properties of materials that produce those well-known behaviors.

Now, by scrutinizing atoms’ wily ways, scientists are devising new techniques to cut down on friction, going beyond known slippery surfaces like ice, Teflon and the banana peel of countless comedy gags. Some scientists have found ways to bring friction down to near-zero levels, a property known as superlubricity. Others are studying quantum effects that reduce friction.

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Category: Science