Worth knowing before you need it
Answers that can save you money, time, or a great deal of trouble
Why don't birds get electrocuted on power lines?
Electricity only flows when there is a voltage difference across something, and a bird touching one wire has both feet at the same voltage, so there is nothing to push current through it.
Why do phishing emails still work on careful people?
They do not target carelessness — they target context, arriving at a moment when the request they make is exactly what you were expecting.
Why does water make a pan fire worse?
The oil is hotter than boiling water by hundreds of degrees, so the water flashes into steam instantly and blasts the burning oil upward and outward as a fireball.
Why can't a website tell you your forgotten password?
A well-built site never stored your password in the first place — only a one-way scramble of it, which can be checked against but cannot be turned back.
Why are airplane windows round?
Sharp corners concentrate stress into a single point, and at cruising altitude a pressurised cabin pushes hard enough on that point to tear the fuselage open.
Why do websites need cookies?
The web was designed to forget you between every click, so a cookie is the note the site hands you to carry back, because it has no other way to know you are the same person.
Why does saving early beat saving more later?
Money you invest early spends longer earning returns on its own returns, and that compounding grows with time in a way that later contributions cannot catch up with.
Why do cars have crumple zones?
Making the ends of the car fold on impact stretches the crash over a longer moment, and a longer moment means a smaller force on the people inside.
Why does bread go stale faster in the fridge?
Staling is starch slowly re-crystallising rather than bread drying out, and that crystallisation runs fastest at exactly the temperature a fridge holds.
Why does braking distance quadruple when you double your speed?
Stopping means getting rid of kinetic energy, and that energy grows with the square of speed — so twice as fast is four times as much energy to shed.
Why do tyres have treads?
Not for grip — a smooth tyre grips a dry road better. The grooves exist to give water somewhere to go, so the tyre can still touch the road in the rain.
Why do carbon monoxide alarms matter when smoke alarms already exist?
Carbon monoxide has no smell, no colour and no smoke, and it binds to your blood hundreds of times more readily than oxygen — so nothing you can sense tells you it is there.
Why can a paracetamol overdose be deadly even when you feel fine?
The damage is done by a chemical your liver makes while breaking the drug down, and it destroys liver cells for a day or more before you feel anything at all.
Why do bridges have expansion joints?
Steel and concrete get longer when they warm up, and a bridge with nowhere to put that extra length will either buckle or tear itself apart.
Why do SSDs wear out?
Every write forces electrons through a thin insulating layer, and each crossing damages that insulation slightly until the cell can no longer reliably hold a charge.
Why can't websites read files on your computer?
Browsers run every page inside a deliberately powerless sandbox, because the alternative — letting arbitrary code from strangers touch your filesystem — would make visiting a link as dangerous as running a downloaded program.