# Second FAQs:

Q: Is a second the SI base unit of time?

A: Yes, and commonly understood and historically defined as 1/86,400 of a day - this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each.

Q: Are seconds usually counted in hours and minutes?

A: Yes.

Q: Are seconds : an hour is 3600 seconds?

A: Yes, a day is 86,400 seconds, a week is 604,800 seconds; a year is about 31.

Q: Is a second 9,192,631,770 cycles of the radiation that gets an atom of cesium-133 to vibrate between two energy state?

A: Yes, and ,192,631,770 cycles of the radiation that gets an atom of cesium-133 to vibrate between two energy states.

Q: Was a second thus defined as "the fraction ​1⁄31,556,92"?

A: Yes, and hus defined as "the fraction ​1⁄31,556,925".

Q: Was a second selected to correspond exactly to the length of the ephemeris second previously defined?

A: Yes.

Q: Are seconds : a stone falls about 4.9 meters from rest in one second?

A: Yes, a pendulum of length about one meter has a swing of one second, so pendulum clocks have pendulums about a meter long; the fastest human sprinters run 10 meters in a second; an ocean wave in deep water travels about 23 meters in one second; sound travels about 343 meters in one second in air; light takes a fraction over one second to reach Earth from the surface of the Moon.

Q: Are seconds not exactly equal to atomic seconds is UT1?

A: Yes, and a form of universal time.

Q: Was a second redefined in terms of a year relative to that epoch?

A: Yes.

Q: Is a second usually denoted in decimal notation, i.e?

A: Yes, 2.01 seconds, or two and one hundredth seconds.

Q: Is a second usually counted in tenths or hundredths?

A: Yes.

Q: Is a second counted in milliseconds?

A: Yes, and microseconds , nanoseconds , and sometimes smaller units of a second.

Q: Is a second added to clock time every once in a while to keep clocks in sync with Earth's rotation?

A: Yes.

Q: Are seconds an unsigned clock depicting Orpheus in the Fremersdorf collection?

A: Yes, and dated between 1560 and 1570.

Q: Is a second a 1-gigahertz microprocessor which has a cycle time of 1 nanosecond?

A: Yes.

Q: Is a second also part of several other units of measurement like velocity?

A: Yes, and acceleration, and frequency.

Q: Is a second part of other units, such as frequency measured in hertz , velocity and acceleration?

A: Yes, The metric system unit becquerel, a measure of radioactive decay, is measured in inverse seconds.

Q: Are seconds usually expressed as minutes and seconds, or hours, minutes and seconds of clock time, separated by colons, such as 11:23:24, or 45:23?

A: Yes, It rarely makes sense to express longer periods of time like hours or days in seconds, because they are awkwardly large numbers.