Put your hands together. Now move them back and forth to rub them against each other. Feel that heat? That’s from friction. No matter if it’s between siblings or the gears of an engine, we usually think of friction as a bad thing, and often it is. Friction can cause things to heat up, wear down, and eventually break apart. To fight friction, we apply lubricants like oil (though I wouldn’t advise doing so to your siblings, as it will probably just make things worse).

Lubricants coat interacting surfaces and make it easier for them to slip past each other. There’s a whole scientific and engineering discipline dedicated to the materials science, chemistry, physics, and mechanics of friction, wear, and lubrication. It’s called tribology, which comes from the Greek word tribos—to rub. Tribologists like me are usually trying to save people money by keeping things from wearing out, but our skills can come in handy when people are making money, too.

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