Learn something in five minutes
Short, complete, self-contained
Why is the sky blue?
Air molecules scatter short-wavelength light far more strongly than long-wavelength light, so blue arrives at your eye from every direction of the sky while red passes straight through.
Why can't you tickle yourself?
Your brain predicts the sensations your own movements will produce and quietly turns them down, so a self-administered tickle arrives already expected and therefore not ticklish.
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 'mama' and 'papa' sound similar in almost every language?
Because babies everywhere babble the same easiest sounds first, and adults everywhere hear those sounds as being about them and adopt them as words.
Why do mirrors flip left and right but not up and down?
They do not flip left and right at all — they flip front and back, and you are the one who mentally rotates yourself to face your reflection.
Why do we get goosebumps?
A tiny muscle at the base of every hair yanks the hair upright when you are cold or startled — useful if you are covered in fur, and left over in us because we are not.
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 onions make you cry?
Cutting the onion mixes two chemicals it kept apart, and the reaction makes a volatile gas that turns mildly acidic on the wet surface of your eye.
Why does food taste bland on planes?
The cabin is drier than a desert and pressurised to a mountain altitude, which dulls your sense of smell — and constant loud noise suppresses sweetness on top of it.
Why do keyboards use QWERTY?
It was designed around the mechanical constraints of a machine nobody uses any more, and it survived because everyone had already learned it.
Why can't you divide by zero?
Division asks what you must multiply by to get back where you started, and multiplying by zero destroys that information — so the question either has no answer or has every answer.
Why do some countries drive on the left?
Left was the older custom across much of the world, and the countries that changed did so because of specific historical pressures — mainly Napoleon, and later the pull of neighbours and American vehicles.
Why do prices end in .99?
People read prices left to right and stop paying attention early, so £9.99 lands in the mind as 'nine something' rather than 'basically ten'.
Why does ice float on water?
Freezing forces water molecules into an open framework with gaps in it, so the same molecules take up about a tenth more room as ice than as liquid.
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 bruises change colour?
A bruise is blood spilt under the skin, and the colours are the stages your body's clean-up crew takes it apart in.
Why do computers use binary?
Because it is far easier to build a component that reliably tells apart two states than ten, and reliability is what matters when you are switching billions of times a second.
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 is the ocean salty?
Rivers carry dissolved rock into the sea, and then only the water leaves again — evaporation takes the water and leaves the salt behind, over billions of years.
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 we have leap years?
A year is not a whole number of days, so the calendar has to be given an extra day now and then or the seasons slowly drift away from the dates.
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 elevators have mirrors?
Mirrors were added because complaints about slow elevators dropped sharply when people had something to look at, which was far cheaper than making the elevators faster.
Why do photos of propellers look bent?
Most digital cameras do not capture the whole image at one instant — they scan it line by line from top to bottom, so anything moving fast is recorded at a slightly different position in every row.
Why are rockets launched eastward?
The Earth's surface is already moving east at up to about 1,670 km/h at the equator, and launching in that direction means the rocket starts with that speed for free.