A storm flashes and booms — which one gets to you first?
Look up high… a storm cloud! A storm makes two things — a bright flash you see, and a big boom you hear. Watch… there goes the flash. The whole sky lit up! Now the boom is on its way to you. So tell me… when do you think the boom gets to your ears — right now, or after a little wait? Have a guess!
After you watchA storm flashes and booms — which one gets to you first?
The short answer
The flash gets to you first. A storm makes the flash and the boom at the very same time, but light zips to your eyes right away while the sound of the boom is much slower, so it takes a little while to travel to your ears.
Try this next
- What if the storm is very close instead of far away? Next storm, guess first whether the boom will come quickly or after a long wait, then count slowly between the flash and the boom to find out how close it is.
- What happens with fireworks far across the sky? Watch a faraway firework. Guess first if the bang comes right with the flash or a bit after, then watch and listen to check.
The whole story
How it works
Lightning makes a flash of light and a clap of sound at the same instant. Light is incredibly fast, so the flash reaches your eyes almost the moment it happens. Sound is far slower — it has to travel all the way through the air to your ears, which takes time. So you always see the flash first and hear the boom a little later. The farther away the storm is, the longer the boom takes to arrive, so the bigger the wait between the flash and the boom.
What people get wrong
Lots of little kids think the boom comes at the same moment as the flash, or even that the flash makes the boom happen after it. Really the flash and the boom start together. You only see the flash first because light is so much faster than sound, and the boom shows up later because it is slowly traveling to your ears.
The catch
Because the boom is slow, you can use the wait to feel how close a storm is — a quick boom means it is close, a long wait means it is far. But hearing the boom at all means the storm is near enough to be a little bit scary, so it is always a good time to be cozy inside with a grown-up.
Questions kids ask
Why do you see the flash before you hear the boom?
Because light is much faster than sound. The flash zips to your eyes almost right away, but the boom's sound travels slowly through the air, so it reaches your ears a little later — even though the storm makes them both at the same time.
Do the flash and the boom happen at the same time?
Yes! The storm makes them together in one instant. You just see the flash first because light wins the race to you, and the boom takes a little while longer to travel to your ears.
Why is the wait longer when the storm is far away?
Because the slow boom has farther to travel. A close storm's boom gets to your ears quickly, but a far storm's boom has a long trip through the air, so you wait longer to hear it.
Talk about it
- Guess first: when there is a storm, do you think you see the flash first or hear the boom first? Why?
- The flash and the boom start together — so why do you think the boom shows up later?
- If a boom comes very quickly after the flash, is the storm close or far away?
For grown-ups
Light travels at about 300,000 km/s, so over storm distances the flash arrives effectively instantly. Sound travels at only about 343 m/s — roughly 1 kilometer every 3 seconds — so the flash-to-boom delay is essentially the sound's travel time. The farther the storm, the longer that delay, which is the basis of counting the seconds between flash and thunder to estimate distance. For a 4–6-year-old, the takeaway is simply: light wins the race to you, so you see, then hear.
Keep going
What else makes you wonder?
- Fireworks pop in the sky with a flash, then a bang. Why do you hear the bang a little after?
- When someone far away claps or hammers, you see it, then hear it. Why?
- If the boom is slow, what other slow sounds take a while to reach your ears?