How does a touchscreen know?

First secret: you carry electricity. Your body is full of salty water, and salty water carries charge — so your skin is a soft wet wire that can sip a little.

Tiny gold charge dots rise out of a glass of salty water and travel along the inside of a child's arm like beads in a wire, all the way out to the fingertip.

Second secret: the glass hides a grid. Tap to switch it on — tiny squares each hold a puddle of charge, waiting for something to sip from them.

tap to see the hidden grid

Two kinds of touch. A finger or a metal spoon is a conductor — it sips charge from the square it lands on. A plastic tip is an insulator — it touches, but no charge flows.

Two panels: on the left a coral fingertip lifts gold charge dots up out of a blue grid square so its puddle shrinks; on the right a grey-blue plastic tip touches an identical square but no charge moves.

Your turn. Pick a toucher, then tap a spot on the screen — watch the charge meter.

⚡ charge the grid feltnothing yet

A conductor sips charge; an insulator can't. Tap and see.

But you never tried pressing…

A hand in a thick grey-blue wool glove presses down hard on a phone's blue glass screen, with three big arrows pushing straight down and squish lines around the flattened fingertip.

Put on a thick wool glove and mash the screen as hard as you can. Surely all that force pushes a touch through… 🤔

You just saw: only a conductor can sip charge.

Wearing a thick wool glove, you press the screen as hard as you can. Does it notice your tap?