why questions · Ages 9-12

Why Do We See Lightning Before We Hear Thunder?

Light travels much faster than sound, so the flash reaches our eyes almost instantly while the thunder takes seconds to cross the air.

The whole story

1. Maya stood at the farmhouse door with her weather notebook tucked under one arm. A white flash split the clouds, and she began counting before the thunder arrived.

2. One second passed. Then two. Then three. At last, thunder rolled across the hills, deep enough to tremble in the window glass.

3. Maya asked her grandfather whether the sky was making two separate signals. He checked his pocket watch and smiled. “The flash and the boom begin together,” he said. “They simply do not travel together.”

4. Grandfather stretched a ribbon across the porch. “Imagine this ribbon is the air between us and the lightning,” he said. “Both messages start at the same place, but each moves through that distance at its own speed.”

5. They made a simple test. The lantern would stand for light, and the bell would stand for sound. Maya wrote down her guess, then rubbed out the first answer and wrote a new one.

6. Grandfather lifted the lantern’s cover. Maya saw its glow at once. She waited, holding her breath, but no bell had rung.

7. A moment later, the bell rang. The light had crossed the space first; the sound had followed behind it.

8. Maya drew two paths from the storm to the farmhouse. The light’s path was almost impossibly quick. The sound’s path took longer because sound travels through the air much more slowly.

9. Another flash opened the clouds. Maya counted three seconds before the thunder arrived. This time, she did not wonder whether the sky had paused.

10. Light travels much faster than sound, so the flash reaches our eyes almost instantly while the thunder takes seconds to cross the air.

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