How do we know that 1 second is 1 second?
How long is 1 second? How is 1 second measured?
What is 1/2 times 1/2? How many consecutive days does 1 million seconds equal? How is a second meausred? What is the difference between meters per second and meters per second²? Which is correct: 1.5 hour or 1.5 hours? Why? What is 1/3 of 60? How many degrees does the hour hand of a clock move in one second? What is the Five-Second Rule? How does it work? When people say "in a couple of days" how many days do they mean? What is 5 times 1/2? Can time be measured by any another unit than hours, minutes or seconds? How many degrees does the hour hand of a clock move in a second? How many meters is 1 square meter? What is the 20 second rule? How far can one see with the naked eye? How is this calculated? Why is time measured in seconds, minutes and hours? What fraction of a minute is 21 seconds? How is extra time calculated in soccer/football? At what time between 5 and 6 o’clock are the hands of a clock 3 minutes apart? If I read 1 1/2 pages in a book in 3 1/3 minutes how many pages will I have read in 1 minute? When did we start measuring time in seconds? Who decided what duration will be one second? Why did we divide an hour in 60 minutes and a minute in 60 seconds? Why not 100 minutes or 100 seconds? How did this system come to exist? How many 2/7 are there in 5/6? What frames per second do the human eyes run at? How many inches in one feet? Why is time calculated in 60 minutes per hour and 60 seconds per minute? Why can't it be 100 minutes per hour? What is the angle between the hands of hour and minute at 6:35? How many inches are in a metre? In one day, how many times do the minute hand and the second hand of a clock make a straight line? Are 1/2 and 2/4 the same number? How many one fifth make a whole?