Why does some thunder crack but other thunder rumbles?
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After you watchWhy does some thunder crack but other thunder rumbles?
The short answer
Thunder is sound from rapidly heated air along a lightning channel. Sounds from its different parts can reach you together or at different times, producing a short burst or a rumble. Channel shape, orientation, air, and reflections all matter.
Try this next
- Why do the two sides match? Pair each channel point with the point the same distance across the middle. Compare their paths to the two ears.
- What if the channel were vertical? Sketch the paths to the top and bottom and predict how the arrival spread changes.
The whole story
How it works
Our simplified model fixes a 600 m horizontal channel 700 m above ground. Below its middle, path lengths are relatively similar; far to one side, they differ more. Dividing each path by the speed of sound gives each arrival time. This is one geometry, not a universal rule that every nearby bolt has equal path lengths.
What people get wrong
A rumble is not simply a quiet crack, and distance alone does not explain every thunder sound. The orientation and shape of the channel change the paths to the listener.
The catch
The model isolates path delays. Real thunder also includes branches, multiple strokes, reflections, atmospheric effects, and changing loudness. Never use a gentle rumble as a signal that lightning is safe.
Questions kids ask
Does a rumble always mean lightning is far away?
Distance affects thunder, but channel geometry, reflection, and atmospheric effects matter too. Any thunder means lightning is close enough to be dangerous.
What does this model isolate?
It compares travel times from one horizontal channel to an ear at different lateral positions. It holds channel shape, height, emission time, and sound speed fixed.
Why can one lightning flash make a long sound?
Sound comes from many channel segments. Their different path lengths and reflections can deliver it to your ear over an extended time.
Talk about it
- What stayed fixed in this model?
- Which path was shortest at each ear position?
- Why might a different lightning shape give a different result?
For grown-ups
Model delay for a channel point x and lateral ear position d is sqrt((d-x)^2+700^2)/343 seconds, with x from -300 to 300 m. The spread of delays sets the modeled burst duration. Real channel orientation and propagation conditions add effects omitted here.
Keep going
What else makes you wonder?
- What if the channel were vertical instead of sideways?
- Could a reflected path make a second burst arrive later?
