speed of light definition
The distance light can travel in a unit of time through a given substance. Light travels through a vacuum at about 186,000 miles, or 300,000 kilometers, per second. (See E = mc2, electromagnetic waves, relativity, and twin paradox.)
Note: A light year, or the distance light can travel in a year, is over five trillion miles.
Note: Light from the sun takes about eight minutes to reach the Earth.
Note: Light from the moon, and other electromagnetic radiation from the moon, takes about a second and a half to reach the Earth. In conversations between astronauts on the moon and their ground crews, there are lapses of about three seconds between exchanges, because of the time it takes for radio waves to make a round trip between the Earth and the moon.
Note: The special theory of relativity states that the speed of light as measured by all observers is the same.
noun 1. an instrument on an automobile or other vehicle for indicating the rate of travel in miles or kilometers per hour. noun 1. a device fitted to a vehicle to measure and display the speed of travel See also mileometer speedometer (spĭ-dŏm’ĭ-tər) An instrument for indicating the speed of a vehicle, typically by measuring […]
- Speed ramp
noun 1. (Brit) a raised band across a road, designed to make motorists reduce their speed, esp in built-up areas
verb (used with or without object), speed-read [speed-red] /ˈspidˌrɛd/ (Show IPA), speed-reading [speed-ree-ding] /ˈspidˌri dɪŋ/ (Show IPA) 1. to read faster than normal, especially by acquired techniques of skimming and controlled eye movements.
noun, Automotive Informal. 1. a garage that specializes in fitting cars, especially hot rods, with custom-made mechanical equipment for racing.