Speed of Sound and Light

Most recent answer: 2/14/2017

What are speeds of sound and of light . We are doing research on lightning and thunder .
- Holly Harper (age 9)

The speed of sound through air is about 340 meters per second. (The speed of sound in water is about 4 times faster than this). The speed of light in air is about 300 million meters per second.


(published on 10/22/2007)

Follow-Up #1: light/sound time lag

If you see a flash of light and it takes 5 seconds before you here the noise how far is that flash away from you
- Anonymous
Hendersonville NC
The distance depends on the speed of sound in air.   This speed varies slightly depending on the temperature, pressure and humidity.   For ’back of the envelope’ calculations you can take
V = 340 km/sec.   The distance-speed-time relationship is d = V*t.  So plugging in the numbers you get 1700 meters, a tad over one mile.

Lee H

(published on 10/22/2007)

Follow-Up #2: light and sound

how do we know light travels quicker than sound
- katrina (age 12)
When there's a big lightning strike, you see it first, then hear it a little later.

Mike W.

(published on 05/16/2013)

Follow-Up #3: The difference in time taken

explain the difference in time taken for light and sound to travel the same distance
- katie (age 11)


The time taken to reach a particular distance (in most general sense) depends on how fast someone is moving. The speed of light is much faster than the speed of sound in air. If you want to compare, the speed of sound in air is ~ 343 m/s and the speed of light is 3x1010 m/s. In other words, light travels 186 thousand miles in 1 second, while sound takes almost 5 seconds to travel 1 mile.


(published on 02/14/2017)