A storm, far off.
The flash arrives. Then the bang. Why the wait?
Eve can say this.
The flash arrives. Then the bang. Why the wait? Move the storm. Watch the gap. Count from a room. Do not go looking for the storm.
Words Eve says
The flash arrives. Then the bang. Why the wait? Move the storm. Watch the gap. Count from a room. Do not go looking for the storm.
Count from a safe room, not from a field
This is a simulation. Do not chase storms, stand under trees, or wait on a hill to count. If you hear thunder, you are close enough to be reached. Go inside.
Do not go looking for a storm. If you are already inside, and lightning is happening far off, you may count.
Fireworks with a grown-up are a kinder version of the same idea: bloom, wait, bang.
If the bang follows the flash almost at once, the storm is close. Stay inside.
What else arrives as light first, sound later?
Look closer
Notice
You see the lightning almost as it happens.
The thunder is the same event, arriving later.
If the wait gets longer, the storm is farther. If the wait shrinks, it is closer.
What do you think will happen?
If the storm is farther away, what happens to the wait between flash and bang?
Change how far the flash is.
Keep looking
What must be true?
Light is so fast that, across a storm, it might as well arrive now.
Sound in air is much slower, about a mile every five seconds, or a kilometer every three.
The wait is the sound catching up. The flash and the bang are the same event, split by speed.
Two speeds, one event.
Light in air travels about 300,000 kilometers every second. Sound in room-temperature air travels about 343 meters every second. That is why a distant firework blooms in silence, then thumps. NOAA’s rule of thumb: count the seconds from flash to bang, divide by five, and you have miles. Divide by three, and you have kilometers. It is an approximation. Temperature changes the exact speed of sound. It is good enough to tell close from far.
The flash arrives. Then the bang. They are the same event. Light is so fast it might as well arrive now. Sound in air is slower, about a mile every five seconds. The wait is the sound catching up. Count from a room. Do not go looking for the storm.
Words Eve says
The flash arrives. Then the bang. They are the same event. Light is so fast it might as well arrive now. Sound in air is slower, about a mile every five seconds. The wait is the sound catching up. Count from a room. Do not go looking for the storm.
The same lightning, two arrivals
People have long known the flash comes first. Sailors used the gap as a rough measure of distance.
The National Weather Service still teaches flash-to-bang as a safety habit: the count tells you how far, and “if you hear it, clear it.”
The physics is older than the slogan. Two speeds. One event.
- NOAA: Determining distance to a thunderstorm · About a mile every five seconds, a kilometer every three. Temperature changes the exact speed.
- National Weather Service: Thunder · Thunder is the sound of the flash. Count, then go inside if it is close.
- Encyclopaedia Britannica: Speed of sound · The speed of sound in air depends on temperature. 343 m/s is a typical 20 °C figure.