ANSI/IEEE Device Numbers. Protective relays are commonly referred to by standard device numbers. For example, a time overcurrent relay is designated a 51 device, while an instantaneous overcurrent is a 50 device. Multifunction relays have combinations of device numbers. A 27/59 device, for example, is a combination under/over voltage relay.
At 0Â° Celsius the speed of sound in U.S. textbooks is 331.3 m/s. At 20Â° Celsius the speed of sound then is 343.21 m/s, rounded 343 m/s. At 0Â° Celsius, the speed of sound in German textbooks is 331.5 m/s. At 20Â° Celsius the speed of sound then is 343.42 m/s, rounded 343 m/s.
Chuck Yeager and the X-1 research plane that broke the sound barrier in 1947. It can be seen today at the Smithsonian Air & Space Museum in Washington, D.C. The speed of sound varies depending on the temperature of the air through which the sound moves. On Earth, the speed of sound at sea level â assuming an air temperature of 59 degrees Fahrenheit (15 degrees Celsius) â is 761.2 mph (1,225 km/h). Because gas molecules move more slowly at colder temperatures, that slows the speed of sound; sound moves faster through warmer air.