Learn something in five minutes
Short, complete, self-contained
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 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 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 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.