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Lesson 8: Time

# Telling time (unlabeled clock)

Sal tells time on unlabeled analog clocks. Created by Sal Khan.

## Want to join the conversation?

• Is it smarter idea to learn time on a digital watch before an analog watch that tells you the time?
(8 votes)
• I agree. It is good to be able to tell time the harder way.
(6 votes)
• When we write time dose the mins come first
(0 votes)
• The order is hours, minutes, and seconds. Usually just hours and minutes are used.
(17 votes)
• why do we need A.M. and P.M.?
(4 votes)
• We need AM and PM to calculate the days and hours. “AM” stands for the Latin phrase Ante Meridiem —which means “before noon”—and “PM” stands for Post Meridiem : “after noon.”" So if you think of it as AM means morning and PM means night.

Hope this helps!
(3 votes)
• where did 60 seconds in minute, 60 minutes in a hour, and 24 hours in a day come
(4 votes)
• Ancient Babylonians. They used number base 60 (Sexagesimal).
(6 votes)
• does the second minute hand always move when the second hand counts 60 seconds because it doesnt look like it
(2 votes)
• It sure does. The minute hand will move to the next minute after 60 seconds.
Example:
If the minute hand is on 1, it will be on minute 2 after the second hand counts 60 seconds.
(4 votes)
• I'm having trouble with this problem.

Bob played video games for 15 hours and 23 minutes. He stopped playing on Wednesday morning, . What time did Bob start playing?
(2 votes)
• Start with minutes. First find out how long Bob had played at by withdrawing 5 minutes from 23 minutes.
First: 23 - 5 = 18 So at Bob had played for 15 hours and 18 minutes.

Then with draw 18 minutes from 60 minutes, because 1 hour is 60 minutes.
Therefore: 60 - 18 = 42 So at Bob had played for 15 hours.

Lastly workout the hours. First withdraw 6 hours from 15 to work backwards to midnight.
First: 15 - 6 = 9 So at Bob had played 9 hours.

Then set midnight as 12 and minus 9 hours to find the starting time.
12 - 9 = 3 Therefore Bob started playing at in the afternoon.
(3 votes)
• why is time different in different parts of the world shouldn't it just be the same?
It would be a lot less confusing.
(2 votes)
• Yes but say if you were in China and someone was in America. For example, AM in America.
For some places at that time, the sun may be setting or just rising.
They also have different time zones so you could have an average like AM -- PM and you could use as much as the daylight as possible.

As mentioned on http://www.timeanddate.com/time/time-zones.html, here's a more in-depth reason:

"Many towns and cities around the world used to set clocks based on observing the sun and the stars. This occurred prior to the late 19th century. Dawn and dusk occur at different times at different places because of the Earth’s rotation. However, time differences between distant locations were barely noticeable because of long travel times and the lack of long-distance communications. The expansion of transport and communications, as well as trade globalization, during the 19th century created a need for a more unified time-keeping system."
(3 votes)
• Is 13 in 24 hour time 1 AM?
(1 vote)
• No it's 1 PM. It works very easily actually when you think about it. Hour 1 in military time (24 hour time I suppose you could say) is 1 AM, the first hour of the day. So 13 hours threw the day would get you to 1 PM. If you can subtract 12 from the number it is in the PM if not it's in the AM. The actual time is minus 12 then just add PM. So again 13-12=xPM x being the number with PM on the end since you can subtract a 12 from 13.
(3 votes)
• if it takes Earth 24 hours to spin all the way around (360 degrees) than how many hours, days, weeks, months, or years does it take for Jupiter to completely turn around?
(1 vote)
• Believe it or not, Jupiter actually spins really fast, fast enough that 1 complete rotational period is 10 hours! These speeds also contributes to the constant storms on Jupiter, as well as the Giant Red Spot.
(3 votes)
• How we say the time differs in languages. I speak three languages and others say ''five without 10''. So these videos are teaching the time in english right?
(1 vote)
• This site works in English, primarily, but it has some translate options as well
(2 votes)

## Video transcript

We're asked, what time is it? So first, we want to look at the hour hand, which is the shorter hand, and see where it is pointing. So this right over here would have been 12 o'clock, 1 o'clock, 2 o'clock, 3 o'clock, 4 o'clock. And it looks like it's a little bit past 4 o'clock. So we are in the fourth hour. So the hour is 4. And then we have to think about the minutes. The minutes are the longer hand, and every one of these lines represent 5 minutes. We start here. This is 0 minutes past the hour, then 5 minutes past the hour, then 10 minutes past the hour. So the time is-- the minutes are 10, 10 minutes past the hour, and the hour is 4, or it's 4:10. Let's do a few more. What time is it? So first, we want to look at the hour hand. That's the shorter hand right over here. It's at-- let's see. This is 12, 1, 2, 3, 4, 5, 6, 7, 8, 9. And it's between 9 and 10. It's just past 9. So it's still in the ninth hour. It hasn't gotten to the 10th hour yet. The ninth hour's from starting with 9 all the way until it's right almost before it gets to 10, and then it gets to the 10th hour. So the hour is 9, and then we want the minutes. Well, we can just count from 0 starting at the top of the clock. So 0, 5, 10, 15, 20, 25, 30. It's 9:30. And that also might make sense to you, because we know there are 60 minutes in an hour. And this is exactly halfway around the clock. And so half of 60 is 30. Let's do one more. What time is it? So let's count. This is 12, 1-- actually, we can even count backwards. We can go 12, 11, 10. So right now we're in the 10th hour. The hour hand has passed 10, but it hasn't gotten to 11 yet. So we are in the 10th hour. And how many minutes past the hour are we? So this would be 0, 5, 10, 15, 20 minutes past the hour. That's where the longer hand is pointing. It is 10:20.