Tove sees lightning flash outside her window. Seconds pass before the thunder arrives. The flash and the rumble left the same strike together.
They arrived apart because the two waves travel at wildly different speeds. This lesson puts numbers beside the difference.
Light crosses air at very nearly its vacuum speed, 3.00 × 10⁸ m/s.
Sound crosses air at about 340 m/s.
Across the distance of a storm, the flash arrives almost at once, while the thunder takes seconds.
That is the whole story of the gap Tove noticed: one strike, two waves, two speeds.
The speed gap is one more way to tell the families apart: electromagnetic waves are far faster than mechanical waves.
So for any far-off bang or blast, you see it first and hear it later.
Across a wide canyon, Tove watches a ranger chop wood. She sees each strike land before she hears its thud. Why?
The strike's light crosses the canyon at very nearly 3.00 × 10⁸ m/s.
The thud's sound crosses the same air at about 340 m/s.
Light is roughly a million times faster, so the sight arrives far sooner.
She sees each strike before she hears it because the light arrives almost at once and the sound takes its time.
Using the speeds in the table, say roughly how many times faster light is than sound in air.
Light: 3.00 × 10⁸ m/s. Sound: about 340 m/s.
Comparing the two speeds gives a factor of roughly a million.
Light is roughly a million times faster than sound in air.
Selby watches a distant firework burst, then hears the bang a few seconds later. Why does the bang arrive after the burst's light?
How does the speed of light compare with the speed of sound in air?
Rurik says: 'Light travels roughly a million times faster than sound travels through air.' Is Rurik correct?
From the far bleachers, Rurik watches a batter hit a home run. Which reaches him first: the sight of the hit, or its crack?
Two waves set out together across 10 km of air. One arrives in a tiny fraction of a second; the other arrives about 30 seconds later. Which statement identifies the waves?
Quenby sees the dust fly up from a distant quarry blast about 9 seconds before she hears its boom. Why does the sight arrive so much earlier?