01Science

A wing holds a plane up by throwing air downward

Stick your hand out of a car window and tilt it up slightly. The air gets deflected down off your palm, and your hand gets pushed up. A wing does the same, harder, with a curved top surface that bends the passing air downward too. Push air down, the air pushes you up. The school story that air splits at the front and must meet again at the back is simply wrong, and it is not why wings work.

Explains why planes can fly upside down and why a paper plane with flat wings flies at all.

02Tech

GPS satellites just broadcast the time, and your phone does the arithmetic

Each satellite carries an atomic clock and shouts out, continuously, where it is and what time it is. Your phone hears that message late, because radio travels at the speed of light and the satellite is thousands of kilometres up. Multiply the delay by light speed and you have your distance from that satellite, which puts you somewhere on a sphere around it. Overlap four such spheres and only one point fits. Your phone never transmits back, and the satellite has no idea you exist.

Clears up the common belief that satellites track you, and shows why GPS works with no signal going up.

03Science

A microwave heats food by flipping its water molecules billions of times a second

Water molecules are lopsided, slightly positive at one end and negative at the other. The oven fills the box with radio waves at 2.45 gigahertz, and their electric field reverses billions of times a second, so the molecules keep twisting to face it. That jostling is heat. The waves only reach a couple of centimetres in, so the centre of a big dish warms by conduction from the outside, not from the inside out.

Explains why food comes out scalding at the edges and cold in the middle, and why stirring halfway helps.

04Tech

A touchscreen finds your finger because your body drains charge from a grid

Under the glass sit two layers of a transparent conductor, laid as fine strips crossing each other like graph paper. Each crossing holds a tiny electrical charge. Your finger is mostly salty water, which conducts, so bringing it close pulls some of that charge away and the chip notices which crossings dropped. No pressure is involved, which is why glass is no obstacle and a feather-light tap works. It also explains why a wool glove or a fingernail does nothing, and why water spilled on the screen produces ghost taps.

Explains every touchscreen frustration you have had, from gloves in winter to a phone going haywire in the rain.

05Science

A battery is a chemical reaction that can only happen through your device

Two different materials sit in a paste or liquid that carries charge. One of them gives up electrons more readily than the other, but electrons cannot cross the paste, so their only route is out through the terminal, along the wire, and through your phone. Inside, charged atoms drift across to balance things out. Flat means the reactants are spent. Recharging drives current backwards to rebuild them, which some chemistries tolerate and others do not.

Shows why a battery holds a fixed amount of stored chemicals, not a quantity of electricity waiting inside.

06Tech

Wifi is radio, and the faster 5 GHz band is the one walls stop

Your router is a radio transmitter running on a fraction of a watt, with your data encoded as rapid changes in the wave. On the 2.4 gigahertz band the waves are roughly 12 centimetres long and get through brick reasonably well. At 5 gigahertz they are around 6 centimetres, carry more data per second, and are absorbed or bounced away sooner. Water absorbs both, which is one reason a room full of people weakens the signal.

Tells you which band to join at the far end of the house, and why moving one room closer fixes so much.

06

That's the set.

All 6 of them. Pick another collection, or go back to today.