📡 Invisible signals

A radio station turns sounds into invisible radio waves and beams them out from a tall antenna. These waves ripple through the air in every direction, and your radio catches them and turns them back into the music and voices you hear. It all travels at the speed of light, so it arrives instantly.

Your phone listens to signals from satellites circling high above the Earth. Each satellite says exactly where it is and what time it sent its signal, and by comparing several of them your phone works out your own spot on the map. It needs at least a few satellites to pinpoint you accurately.

A microwave oven sends invisible waves into the food that make the tiny water bits inside it jiggle very fast. All that jiggling creates heat right inside the food, so it warms from within instead of from the outside. That is why a microwave heats leftovers far quicker than a normal oven.

A touchscreen has an invisible grid of tiny electric sensors just under the glass. Your finger carries a little electric charge, so when you touch the screen it changes the electricity at that exact spot. The device notices which point changed and knows precisely where you tapped or swiped.