Rosehip Mole asked, and Nib — askNib's tutor — drew the answer live at a whiteboard. This is the spoken transcript; enable JavaScript to watch it drawn.
speed of sound
Sound is not instant — it's a wave of squeezed and stretched air, and it takes real time to travel.
In dry air at room temperature, sound travels about three hundred forty three meters per second — that's over a thousand kilometers an hour.
Heat the air up and molecules jiggle faster, bumping their neighbors sooner — so sound actually speeds up as temperature rises.
Sound needs a medium to push through — and denser, stiffer stuff passes the jostle along faster than air ever can.
Here's the fun proof: light is basically instant, but sound crawls — so count the seconds between a lightning flash and its thunder.
Sound covers roughly one kilometer every three seconds — so count five seconds, and the storm is about one mile away.
Sound is a wave racing through matter — fast in warm air, faster in water and steel, and always slower than the flash of light.