Air, a crucial gas surrounding us, possesses a key property: the speed at which sound travels through it. The term “speed of sound” refers to the velocity at which a minor disturbance propagates through a gas. Sound, as we perceive it, is a sensation our brain creates in response to sensory information from the inner ear. The speed of sound in the atmosphere is consistent, varying with the daily temperature. Under standard sea-level conditions, the speed of sound approximates 760 mph, which translates to roughly 1,100 feet per second. This understanding allows us to estimate the distance of a lightning strike.
Lightning produces a bright flash of light, traveling at an astonishing 186,000 miles per second. Therefore, we observe the flash virtually instantaneously. The intense heat from lightning generates thunder, a sound that propagates through the air at the speed of sound. Given the vast difference between the speed of light and the speed of sound, the flash always precedes the thunder.
As depicted, sound waves originate from a lightning strike, moving at about 1,100 feet per second. To calculate the distance traveled by the wave after two seconds, we employ a basic rate equation:
d = s * t
where distance (d) equals speed (s) multiplied by time (t). Thus, after two seconds at 1,100 feet per second, the wave has traveled 2,200 feet. Extend this to five seconds, and the distance becomes 5,500 feet, slightly exceeding a mile (1 mile = 5,280 feet). Since the flash reaches our eyes instantly, counting the seconds between the flash and the thunder allows us to estimate the distance to the lightning strike:
d = 1100 * t (distance in feet)
Alternatively, dividing by 5,280 feet/mile:
d ≈ t / 5 (distance in miles)
Next time you witness a thunderstorm, give it a try! Remember to seek shelter if the time interval is just a few seconds!
