Categories

Electronics & Computers

How does a quartz watch keep time? A quartz watch counts the vibrations of a tiny quartz tuning fork that rings 32,768 times a second. A chip halves that 15 times to get exactly one pulse per second, which steps the seconds hand. How does GPS know where you are? GPS satellites keep sending the time. Your phone measures how long each signal took to arrive, turns that into a distance, and finds the one spot that fits all the distances. A fourth satellite fixes the phone's own clock, and the satellites' clocks are so exact that even Einstein's effect on time has to be corrected. How does a computer count? A computer is full of tiny switches that are either off or on, so it writes every number with just 0 and 1. Each switch is worth double the one to its right: 1, 2, 4, 8. Add up the ones that are on and you have the number.

Weather & Nature

How does fog form? Air always carries some invisible water. On a clear, calm night the ground loses its warmth to the sky and chills the air above it. Cold air can't hold as much water, so the extra gathers on tiny specks of dust and salt as droplets. Billions of them hanging in the air are fog.

Home & Kitchen

How does a toilet flush? A European toilet flushes by releasing a tank of stored water through the bowl and trap, then a float valve refills the tank. A water seal in the trap blocks sewer gas. How does a microwave heat food? A small airless tube in the oven, with a hot wire, magnets and a copper ring, makes invisible waves that a metal channel guides into the box. The metal walls and the net in the door keep them bouncing around inside. The waves make the water in food twist back and forth billions of times a second, and that jostling is heat. The outer layer heats first and the warmth then spreads inwards. How do a fridge and a heat pump move heat? A fridge doesn't make cold. It moves heat out of the box with a loop of pipe and a fluid that boils very easily: a pump squeezes the gas so it gets hot, a hot coil gives the heat away, a tiny gap makes the fluid ice cold, and a cold coil soaks up heat again. A heat pump is the same loop, with the cold coil outdoors and the hot coil heating the house. How does yeast make bread rise? Yeast is a tiny living fungus. In bread dough it eats sugar and gives off gas. Stretchy strands in the kneaded dough trap that gas in tiny bubbles, the bubbles grow and push the dough up, and the oven makes them swell once more before the dough sets around them.

Flight & Motion

How does a helicopter steer? A helicopter's spinning blades are wings. Tilting all of them together makes it climb or sink. Tilting each blade a little more on one side of the circle leans the whole spinning disc, and the helicopter moves that way. A small tail rotor stops the body from spinning. How does a wing create lift? A wing turns the passing air downward and creates lower pressure on top and higher pressure below. Computed airflow, not a cartoon, and why the equal-transit-time story is wrong.

Machines & Mechanisms

How does a zipper work? A zipper is two rows of interlocking teeth and a slider with a Y-shaped channel. See it closing and opening in an x-ray 3D animation. How does a pin tumbler lock work? A cylinder lock is held shut by spring-loaded pin stacks that cross the shear line. See in an x-ray 3D animation how the right key lines up every gap so the plug can turn. How does a speedometer work? A classic speedometer uses a spinning magnet that drags an aluminium cup with eddy currents against a hairspring. Modern cars count pulses from a wheel sensor instead. How does a piano key make a sound? A piano key is a lever that throws a felt hammer at the string. Just before it hits, the escapement lets go, so the hammer flies freely, bounces straight back and lets the string ring. A damper lifts off while the key is down. How does a sewing machine make a stitch? A sewing machine uses two threads. The needle pushes a loop of the top thread under the fabric, a spinning hook carries that loop all the way around the bobbin, and when it is pulled tight the two threads lock together inside the fabric.