ARCHIVE.

The push that drives a rocket happens between the rocket and its own exhaust. Outside air isn't what it pushes against, which is why empty space doesn't stop it.

A gravitational-wave detector rests on glass mirrors hung at the far ends of long laser arms. Its real trick isn't sensing motion. It's stopping almost every other kind of motion first.

Everyone learns that ice is slippery because a thin skin of water coats it. Why that skin forms is a different matter, and the argument has run for nearly two centuries without a winner.

Cool helium far enough and it slips through gaps no ordinary liquid can pass, and creeps up and over the rim of its container. Here's what was actually measured, and the model that makes sense of it.

Nothing with mass can outrun light in empty space. But put light in water or glass and it slows down, and a charged particle that moves faster than that slower light gives off a blue glow. It's called Cherenkov light.

Two spoons sit in the same drawer for a week and end up at exactly the same temperature, yet the metal one feels colder in your hand. Your skin isn't measuring the spoon. It's reporting the temperature of the handshake between you.

Flick water onto a warm pan and it hisses away in seconds. Flick it onto a much hotter one and it beads up and skates around for far longer. Past a certain point, more heat makes the drop last longer, because it's riding on a cushion of its own vapour.

A comet's tail isn't exhaust trailing behind it. It points away from the Sun, wherever the comet happens to be going. And look closely, and there are two of them, because the Sun is pushing on the comet in two quite different ways.

A coffee spill doesn't dry to an even brown blot. It dries to a dark rim around a pale middle, because the drop's edge gets stuck and a hidden current spends the whole drying time carrying the coffee outwards.

In Renaissance painting contracts, one colour got written up like a precious material: ultramarine, made from a stone mined in what is now Afghanistan. The odd part is that crushing the stone doesn't give you that blue. Getting it out took a strange kneading ritual in wax, resin and lye.