People who teach physics often remove friction from calculations to make life easier for students. While that might speed up someone’s homework, it does mean that this all-important force tends to fade into the background, despite it being crucial for our daily lives. Here to bring friction centre stage is Jennifer Vail, a “tribologist” – or studier of friction – at US firm TA Instruments. *Friction: a Biography* is an engaging and wide-ranging book illustrating its many manifestations in the natural world, showing how this force can be harnessed to solve practical engineering problems. Vail, who wrote the book after giving a hugely popular TED talk on friction, does a great job of connecting abstract physical ideas with familiar human experience. I like, for example, her description of what happens when two surfaces slide over each other but the friction between them isn’t constant. As she explains, this “stick-slip” motion isn’t great if you’re trying to inject a drug into someone with a syringe.…