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Current time:0:00Total duration:5:11

CC Math: 4.MD.A.1

Let's talk a little bit
about the US customary units for distance. If we go to a human scale,
the most typical used unit in the US customary
system would be the foot. And as you could
imagine, the term foot, and if you have many of them,
you are now talking about feet, comes from the same
word on the human body. We have a foot or
we have two feet. Now, not everyone's feet
are the same length. But the length of a foot is
roughly a little bit larger than most people's feet. And there are definitely
people whose feet are the size of a foot. And if you're in the
US, you've probably heard of people measuring
their height in terms of feet. So for example, a
slightly above average man of slightly above average height
would have a height of 6 feet. So for example, right over here,
this gentleman right over here was slightly above
average height. His height might be 6 feet. And that might also
be his wing-span. So it would be a distance
something like that. If you wanted to measure things
that are a little bit smaller, say smaller than a foot, or
if we wanted to measure parts of a foot, then you
would go to the inch. And the relationship between
the foot and the inch is that 12 inches are
equal to one foot. So for example, this little
mouse right over here, it might be reasonable
to measure it in inches. On this scale, an inch
might be, depending on the size of
the mouse, an inch might be something like that. And it's also useful
for measuring things like human height,
because very few people are a whole number of feet. They're usually some
fraction of feet. So for example, I am
5 feet and 9 inches. And sometimes this
is denoted as 5, and you have this apostrophe
here, one apostrophe, and then 5 foot 9 inches, and this
is two apostrophes, kind of saying hey, you're going
to the next unit down. These are the inches
right over here. Now if you want to
go to things that are larger than maybe human
scale, we have units for that as well, including the yard. The yard is equal to 3 feet. And 3 feet, well, each
foot is 12 inches, so this is the same
thing as 36 inches. And this is most typically
used for measuring distances of a lot of some kind. And in the United States,
most famously for in football. So your regulation-size football
field, the playing field, the distance between
the end zones, is exactly 100--
I know you can't see my writing there--
is exactly 100 yards. This distance right over here. Right between the end zone. Now, if you want to measure
even longer distances, that's where we go to the mile. And all of these units
are ancient units, going back, actually,
thousands of years. And the mile, based on
the reading I've found, was even used in Roman times. And actually, that's some
of the first examples of this term being used. And it really comes from
the same root word as 1,000, of mil, of 1,000 footsteps
of a Roman soldier. And now, a standard mile
is exactly 5,280 feet. And if you wanted to
figure out this in inches, you could just multiply by 12. But just to get a
sense of a mile, here is a mile on
this map of New York. So if you wanted to put
it right on Manhattan, this distance right over
here is about a mile. So you want to measure really
far distances, either from one point in a city to
another, or maybe even the distance
between cities, or maybe even the
size of the planet, or even the distance from
the Earth to the moon, or something like that, you
will hear that referenced in miles, even the distance
between the Earth and the sun. People say it's
93 million miles. If you're talking about
maybe, a plot of land, you want to measure
its dimensions, or you're talking
about a football field, then yards feel appropriate. If you're kind of
getting to human scale, well, human scale on
one level, but you could get a little bit
larger if you're maybe talking about the
height of a building or something like
that, or you're still talking about measurement
of say, a plot of land, you will still hear people
talk in terms of feet. And if you're measuring
either parts of a foot, or things that are
smaller than a foot, that's when inches
come into play.