Video Transcript
AM and PM
In this video, we’re going to learn
how to tell the time on a 12-hour clock using AM and PM. And we’re also going to learn how
to describe when different activities happen in terms of AM or PM.
Psst! We interrupt this video for a
top-secret message that’s just been delivered. It’s from agent Z. We need to meet
him or her at the park bench at this time here. But there’s a problem with the way
this note has been written. Can you spot what it is? Here’s a clue. Think very carefully about the
information that a clock tells us. We know that the analog clock and
the digital time underneath both show the time half past 10.
We know this because the minute
hand has moved half the way around the clock face. And when it points to the number 6,
it’s a half past time and also because the hour hand is halfway between the 10 and
the 11. So, it’s halfway between 10 o’clock
and 11 o’clock. We also know that there are 60
minutes in an hour. So, if we have a time that is
something 30, we know half an hour has gone by; 30 is half of 60.
So, we know we need to meet agent Z
at half past 10 or 10:30. But which 10:30? We know that every day is 24 hours
long. And a day lasts from 12 o’clock
midnight all the way through to just before 12 o’clock midnight. But we can split our 24 hours into
two lots of 12 hours. We have 12 hours from 12 o’clock
midnight to 12 o’clock midday. Even though it’s dark outside for a
lot of this, we call these morning times. And then, the second lot of 12
hours includes the afternoon and evening or night. Now, it takes 12 hours for the hour
hand to go once all the way around the clock face.
And so in 24 hours, the hour hand
goes round once in the morning and once in the afternoon and the night. In 24 hours, it goes twice around
the clock face. This means that our clock face
looks like this twice in a day: once at 10:30 in the morning, but also at 10:30 at
night. And this is the problem with agent
Z’s message. We don’t know which 10:30 it’s
talking about. Will agent Z be waiting for us at
10:30 in the morning or at 10:30 at night?
Wouldn’t it be good if there was a
way to show whether a time was in the morning, afternoon, or night? Well, did you know? There is a way to do this. And there are no long words to
learn, just four little letters. And two of them are the same, AM
and PM. Now, you don’t need to learn the
next part, but it is interesting. And sometimes, hearing about
interesting things can help us understand things better. So, let’s go back in time, all the
way to ancient Rome.
Now, the Romans spoke a language
called Latin, and a lot of the words we use in maths come from Latin words. Let’s have a quick Latin
lesson. The word “ante” means before, the
word “post” means after, and the word “meridiem” is a time of the day. It means midday or noon. But don’t worry; this is not a
Latin lesson. You don’t need to learn these
words. But they are interesting because
the letters AM stand for the words ante meridiem, and we use this to describe times
before noon. Can you see where the letters PM
come from? They stand for the words post
meridiem, after noon. Maybe, you’ve never stopped to
think about it, but our word “afternoon” means times that are after noon.
Anyway, history lesson over. The only things that we need to
remember are that we can use the letters AM to describe any time in the morning. So that’s from 12 o’clock midnight
all the way through to just before 12 o’clock noon. And the letters PM are used to
describe any time that comes after midday. That’s the afternoon, the evening,
and the night. So, we can write 8 o’clock in the
morning as 8 o’clock AM. But if we want to show we’re
talking about 8 o’clock in the evening, we’d write 8 o’clock PM.
Let’s go back and see whether agent
Z has altered his note. That’s better; he’s going to be
there at 10:30 PM. We know that PM times are times
that are after midday and before midnight. So, we know agent Z is gonna be
waiting for us under cover of darkness. Let’s answer some questions
now. They’re not going to involve any
secret agents, but we are going to need to put into practice what we’ve learned
about AM and PM times. Your mission, should you choose to
accept it, begins now.
The clock shows the time at which
Liam went to bed. Write down the time using “AM” or
“PM.”
We are shown a picture of a clock
here, and we’re told that it shows the time at which Liam went to bed. So, we can imagine him going to bed
looking up at the wall and seeing this time. What time is it? Well, the long minute hand is
pointing up to the number 12. This shows us that it’s a start of
a new hour. This is an o’clock time. And we can also see that the hour
hand is pointing to the number 10. It’s 10 o’clock. And we can write 10 o’clock as a
digital time by writing the hours first, which is 10, and then the number of
minutes. And because it’s a new hour, no
minutes have gone by yet. So, this is how to write 10 o’clock
as a digital time.
Now, we could just write the time
like this, but our question tells us we need to write it using AM or PM. In other words, the answer to our
question is either going to be 10 o’clock AM or 10 o’clock PM. Do you remember what these little
letters stand for? We know that a day is made up of 24
hours. And during this time, the hour hand
goes twice all the way around the clock face. It goes round once during the 12
hours in the morning, this is from midnight to midday, and once during the 12 hours
from the middle of the day through to midnight. This covers the afternoon, the
evening, and the night.
So, we know that Liam’s clock is
going to look like this twice in the day. It’s going to show 10 o’clock in
the morning, but also there’s a 10 o’clock at night. How can we tell which time is
which? This is where the letters AM and PM
come in useful. We use the letters AM to represent
morning times. These are all the times from
midnight until just before noon. And we use the letters PM to
represent afternoon and night times. These are all the times from 12
noon until just before midnight.
Now, there’s one piece of
information in the first sentence that’s going to help us here. The clock shows the time at which
Liam went to bed. Now, unless he’s been awake all
night and he’s gone to bed in the morning, which isn’t very common, it’s probably
fair to think that Liam has gone to bed at 10 o’clock at night. We know that 10 o’clock AM would be
10 o’clock in the morning. And so, we can say that the time
that Liam went to bed is 10 o’clock PM.
Mason walks his dog in the morning
before school. What might the clock look like when
he walks his dog? 8:20 PM, 9:20 PM, 3:30 AM, 7:45 AM,
or 7:45 PM.
This is a really interesting
question because we’re given as possible answers five different times on clocks. But our question only gives us one
very small clue. We’re told that Mason walks his dog
in the morning before school. How can we use this to help us find
the right answer. Let’s take a look at our
clocks. What’s the same and what’s
different?
Well, firstly, we can see that all
of the clocks show digital times. Some of the times look very
similar, don’t they? They’re all made up of a number of
hours and then two dots and then a number of minutes. But can you also see that all of
our times contain two letters? There are three times labeled PM,
and two of the times are labeled AM. Let’s remind ourselves what these
letters mean. There are 24 hours in a day. This means that if we just looked
at the numbers on these clocks, our clock would show the same time twice a day.
For example, let’s think about this
clock here. If we ignore the letters and just
look at the numbers 3:30, we know that there’s a 3:30 in the morning. You probably don’t get to see that
very often because you’re fast asleep. And there’s also a 3:30 in the
afternoon. Now, if we just saw a clock face
that said 3:30, we might not know which time of day it’s talking about. Is it 3:30 in the morning or 3:30
in the afternoon? This is why we use the letters AM
and PM to help.
The letters AM stand for some Latin
words which mean before noon. So, the orange part of our
timeline, that’s all the times from midnight until just before midday, are AM times;
they’re in the morning. And the letters PM stand for some
Latin words that mean afternoon. These are the times on the blue
part of our timeline, from midday or noon all the way through to just before
midnight. This covers the afternoon, the
evening, and into the night.
Now, if Mason walks his dog in the
morning, are we looking for an AM or a PM time? We’re looking for an AM time,
aren’t we? Before noon. This means that although 8:20
sounds like it might be before school, 8:20 PM is actually in the evening. We can forget this time. And we can also forget 9:20 PM. There’s one more PM time at the end
that we can cross out too, 7:45 PM. So, we’re only left with two
possible times in the morning: 3:30 AM and 7:45 AM.
Now, we don’t really need to know
what part of the world Mason lives in or what time his school begins. As we’ve already said, 3:30 AM is
3:30 in the morning, and most of us are asleep at that time. Although we call it 3:30 in the
morning, it’s still very dark outside. It’s the nighttime. I think we can say that Mason isn’t
going to get up in the middle of the night to walk his dog, is he? We know that the letters AM are a
way of showing times that are in the morning. And because we don’t think Mason is
going to walk his dog at 3:30 in the morning, there’s only one other AM time. We know that Mason walks his dog at
7:45 AM.
When William went grocery shopping
in the afternoon, the clock looked like this. What time did he go grocery
shopping?
The clock that we can see in the
middle of the screen shows the time that William went grocery shopping. Do you remember how to read this
time? If we look at the minute hand,
that’s the longer hand to begin with, we can see that it’s pointing to the number
four. If the minute has moved from one
number to the next number on the clock face, it means five minutes have gone by. So, because the minute hand is
pointing to the number four, we can count in fives to see how many minutes have gone
by since it’s an o’clock time. Five, 10, 15, 20. The time is 20 minutes past
something. You can write this as a digital
time as something 20. But 20 past what?
If we look at the hour hand, we can
see that it’s in between two numbers, the numbers three and four. Now we know that at 3 o’clock, the
hour hand would’ve been pointing directly to the number three. But now, it’s on its way to 4
o’clock. It’s not 4 o’clock yet, though. The time is 20 minutes past 3 or
3:20. Now, we could just give this as our
answer. William went grocery shopping at
3:20. But you know, there’s a little clue
in the question that tells us we’re going to need to give a little bit more
information.
We’re told that William went
shopping in the afternoon. And this is important when we’re
talking about reading clocks because there are two 20 minutes past 3 that happen
every day. This means that William’s clock
isn’t going to look like this once a day, but twice a day: once at 20 minutes past 3
in the morning and once at 20 minutes past 3 in the afternoon. Now, we want our answer to describe
20 past 3 in the afternoon. How can we show this?
Well, we can use the letters AM and
PM to help. We use the letters AM to describe
times between midnight and midday. So, 3:20 AM would be 3:20 in the
morning, not long after midnight really. And the letters PM are used to
describe times from midday through to midnight. So, 3:20 PM would be 3:20 in the
afternoon. Can you spot how to answer the
question now? To show that William went grocery
shopping in the afternoon and not the morning, we need to include the letters
PM. The time that he went grocery
shopping is 3:20 PM.
What have we learned in this
video? We’ve learned how to tell time on a
12-hour clock using AM and PM. We’ve also learned how to say when
different events happen using AM and PM.
