Why does some thunder crack but other thunder rumbles?

Same kind of lightning bolt. Sometimes you get one sharp CRACK! and sometimes a long, low rrrrumble that rolls on for seconds. The bolt is a long line that bangs all at once — so what decides whether you hear one quick bang or a drawn-out roll? Let's find the switch.

1Two things to know first

A bolt is a long line, and sound is slow

Before we solve the puzzle, two quick facts about the bolt and about sound. Watch each one move:

The bolt is a tall line

A lightning bolt isn't a dot — it's a long streak of super-hot air. The whole line goes BANG at the very same instant.

Sound takes its time

The flash gets to you instantly, but the bang crawls. Sound only covers about three or four football fields every second — so a far part of the bolt is heard later than a near part.

2The two sounds, side by side

A crack is squished, a rumble is spread

Here are the two things your ears can get from the bolt. Same bangs — but do they land together, or spread out in time?

the CRACK

All bangs land together

Every part of the bolt arrives at once — one tall, sharp spike.

the rumble

Bangs land spread out

The bangs trickle in one after another — a long, low roll.

3Your turn — walk along the ground

Drag yourself and watch the bangs travel

The bolt fires three rings at the same instant — one from the near end, one from the middle, one from the far end. Move yourself and watch whether they reach your ear together or one after another.

side view: the bolt and youtap play to fire the bolt
You are standing: close to the bolt
RIGHT UNDER ITFAR AWAY

4Now make the call

Which spot gives a sharp CRACK?

You're about to drag yourself from right under the bolt out to far away, and listen to what your ear collects. Guess first.

Guess before you find out

The bolt is long, and sound is slow. Which spot makes all the bangs land together as one sharp CRACK — instead of a spread-out rumble?