Topic
Water
12 articles
Physics
Why is a rainbow always in the same place?
Rainbows never turn up in a random corner of the sky. They sit at exactly the same angle from the shadow of your own head, every single time, and the person standing next to you is looking at a different one.
Physics
Why is ice slippery?
Wet glass is not slippery. Cold metal is not slippery. Ice is, even at temperatures where nothing on it could possibly be melting, and the explanation everybody was taught turns out to be far too feeble to work.
Chemistry
Why does wet sand hold its shape?
Dry sand cannot even hold up a small heap. Add a splash of water and the same grains will stand in a tower with vertical walls. Add more water and it collapses into soup, so there is a right amount, and it is far smaller than anybody guesses.
Chemistry
Why can hot water freeze faster than cold?
A schoolboy making ice cream noticed that his warm mix froze before everybody else’s cold mix, and got laughed at for saying so. Sixty years later the argument is still running, which makes this a rare thing — a question you can genuinely still lose.
Chemistry
Why does salt melt ice?
Scatter salt on a frozen step and the ice retreats, even though the salt is exactly as cold as everything else. Nothing has been warmed and nothing has been dissolved away. The salt wins by interfering with traffic you never knew was there.
Biology
Why do your fingers wrinkle in the bath?
Stay in the water long enough and your fingertips fold up like a plum left in the sun, while the back of your hand stays perfectly flat. Same bath, same skin, same half hour. So what decides?
Chemistry
Why does rust make iron swell and crack?
The orange patch on a painted gate does not sink into the metal. It bulges, and the paint around it stands up in a blister that crackles under a fingernail.
Biology
How does a tree lift water to its highest leaf?
The tallest tree alive is taller than a thirty-story building, and the leaves at the very top stay wet all day. No pump ever built can raise water a tenth of that far.
Chemistry
Why does ice float when almost every other solid sinks?
Drop a chip of hard candle wax into a pool of melted wax and it sinks. Almost every solid sinks in a puddle of itself. Ice does the opposite, and one feeble, fussy grip between molecules is the reason.
Astronomy
Why can’t light climb back out of a black hole?
Light is the fastest thing there is, and nothing has ever overtaken it. Yet there are places it sets off from and never leaves. The explanation most people are given was worked out in 1783, and it is wrong.
Physics
Why does a snowflake have six sides?
The pattern that decides the number six is millions of times too small to see, and yet it lands on your sleeve where anyone can count it. Something has to be doing the enlarging.
Chemistry
Why does soap get grease off a plate when water won’t?
Hold a greasy plate under a running tap and the water slides off, leaving the grease exactly where it was. One drop of dish soap and it is gone. Nothing burned it away, and nothing melted it.