This is the smallest
unit of time in everyday use. 60 seconds make up 1 minute and 60 minutes
make up 1 hour. So there are 3600 seconds in 1 hour.
1 second is the
time it takes a world-class sprinter to run 10 metres.
It is also
approximately equal to the time of 1 heart beat!
Light travels at
a speed of 186 000 miles in 1 second.