Physics
Forces, light, heat and sound — the rules everything else has to obey.
19 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 does a spinning coin whirr before it stops?
A coin flattens out, the rattle climbs to a frantic buzz, and then everything ends at once with a slap. Something in there is speeding up while the coin itself is slowing down, and the mathematics says it reaches infinity.
Physics
Why does a whip crack?
A person swings their arm at walking pace and something at the far end of a leather rope breaks the sound barrier. Nothing is exploding and nothing is hitting anything. The bang is a small piece of air being shoved out of the way faster than it can move.
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.
Physics
Why does a bicycle stay up?
Standing still it falls over the moment you let go. Rolling, it will cross a field on its own with nobody on it. Everybody has heard the explanation involving spinning wheels, and somebody built a bicycle specifically to test it.
Physics
Why does helium make your voice squeaky?
Everybody says the gas puts your voice up high. Record it and measure it, and the note you are singing has hardly moved at all. Something else about you got smaller, and it was not your voice.
Physics
Why does toast land butter-side down?
Everybody assumes this is a joke about bad luck, or that the butter weighs one side down. Ten thousand drops by a thousand schoolchildren say it is real, and the culprit turns out to be the height of your kitchen table.
Physics
Why does metal feel colder than wood?
A metal chair leg and a wooden tabletop stand in the same room, in the same air, at the same temperature. Touch them one after the other and your hand insists that one of them is freezing. Your hand is not lying — but it is not measuring what you think it is.
Physics
Why does a desert get so cold at night?
Sand that could blister a bare foot in the afternoon can be chilly enough for a coat by midnight. All that heat goes somewhere, and where it goes is not where most people guess.
Physics
Why doesn’t a spinning top fall over?
Set a top going and it leans at an angle that would flatten anything else on the table, then stays there, drifting round in a slow circle. Nothing is propping it up, and gravity has certainly not let go of it.
Physics
Why can you hear around a corner but not see around one?
A voice from the kitchen reaches you in the hall, around the corner, without any trouble at all. Light from that same kitchen stops dead at the door frame.
Physics
How do noise-canceling headphones erase a sound?
Press one button on a plane and the engine roar drops away, while the passenger beside you stays perfectly clear. Nothing was plugged, and nothing was switched off.
Physics
Why does a mirror swap left and right but not up and down?
Raise your right hand at the bathroom mirror and the person in the glass raises a left one. Nothing in the room has moved sideways. So where is the swap actually happening?
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.
Physics
Why is the back of the fridge warm?
Reach around the back of a refrigerator and the metal is warm. The one machine in the house whose whole job is making things cold turns out to be heating your kitchen, and the reason is sealed inside a pipe.
Physics
Why is the sky blue at noon and red at sunset?
The same sun, the same air, and two completely different colors twelve hours apart. Nothing overhead has been swapped out, so something else must be doing the work.
Physics
Why does thunder rumble on and on instead of going bang?
The flash is over in a heartbeat, but the noise behind it can roll for a dozen seconds. Something is stretching one very short bang into something very long.
Physics
How does sunscreen stop a sunburn?
Rub it in and you can still see your skin, still feel the sun, still get warm. Nothing looks blocked at all. So what has that invisible film actually done?
Physics
Why won’t a wheel full of weights turn forever?
Hang weights around a rim so that one side is always the heavy side, and the wheel should keep falling over itself and never stop. Engineers have drawn that wheel for eight hundred years. Not one has ever run.