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## 4th grade

### Course: 4th grade > Unit 14

Lesson 3: Estimating length# Metric system: units of distance

CCSS.Math:

Sal discusses metric units of length or distance such as millimeter, centimeter, meter, and kilometer. Created by Sal Khan.

## Want to join the conversation?

- Is there any thing smaller then a millimeter?(26 votes)
- exactly how many centimeters are in 1 inch?(you might have to answer with a decimal point)(11 votes)
- There are exactly 2.5 centimeters in one inch.(5 votes)

- If "centi" is to one-hundredth (1/100) and "milli" is to one-thousandth (1/1000), then why is "'milli'on"=1,000,000.(9 votes)
- The metric system has a different way of categorizing measurements and numbers. The romans, a long time ago, created roman numerals.(5 votes)

- Is there anything bigger than a kilometre ?(6 votes)
- 1 Parsec = 30,856,776,000,000 Kilometers

1 Light Year = 9,460,730,500,000 Kilometers

1 Astronomical Unit = 149,597,871 Kilometers

1 Light Minute = 17,987,547 Kilometers

1 Light Second = 299,792.46 Kilometers

1 Mile = 1.609344 Kilometers

1 Nautical Mile = 1.15078 Mile = 1.852001 Kilometer(10 votes)

- Is there any acronym to remember all of the basic units in the metric system?(3 votes)
- Yes! My favorite one is this:
`King Henry Died By Drinking Chocolate Milk`

KING: Kilo(unit)

HENRY: Hecto(unit)

DIED: Deca(unit)

BY: Base (gram/meter/liter)

DRINKING: Deci(unit)

CHOCOLATE: Centi(unit)

MILK: Milli(unit)

Does it kind of develop a permanent fear of chocolate milk in you? Yes. But is it also incredibly helpful? Absolutely!

Hope this helps!(11 votes)

- Yes, many things

For example - An atom is made up of protons, neutrons & electrons which are made up of 3 quarks, but those are just the things that make particles up. There are like 1080 different types of particles! (That's just an understatement) This is where String Theory comes in. String Theory states that all particles are strings that vibrate at a certain frequency and each frequency corresponds to a particle, and how many possible frequencies are possible? ♾️! So we can just say that a particle is a string vibrating at a certain frequency ( probably in the 11th dimension, so if String Theory is true, we live in an 11 dimensional universe) That was a looooooooong comment, wasn't it? Also, check your grammar, it's not "is there anything smaller than a adam" It's "Is there anything smaller than an atom?"(7 votes) - does anyone else wish they had that cute little frog?(6 votes)
- did you know that a light year is 9,460,730,500,000 kilometers(5 votes)
- is there anything bigger than a kilometer(2 votes)
- Good question!

Yes, there are distance units bigger than a kilometer. Some of these units are much bigger!

A mile is 1.609344 kilometers.

A megameter is 1,000 kilometers.

A gigameter is 1,000,000 kilometers.

A terameter is 1,000,000,000 kilometers.

A light year is about 9,500,000,000,000 kilometers.

A parsec is about 31,000,000,000,000 kilometers.

Have a blessed, wonderful day!(7 votes)

- mille is Latin for 100. so why do we say hectometer when we mean 100 meters? why do we say millimeter when we wean a 1000th of a meter?(2 votes)
- mille is not latin for 11. Centa is latin for 100. Centimeter means 1/100 of a centimeter.(6 votes)

## Video transcript

The base unit for distance in
the metric system is the meter. And to get a sense of how long
a meter is, the average human being is between 1.5
and 2 meters tall. So 1.5 meters would be
a not-so-tall person, but 2 meters would
be quite tall. In fact, if you're 2 meters
tall or above 2 meters tall, you might want to
consider basketball. So, for example, in this
drawing right over here by Leonardo da Vinci, if this is
an average-sized male, a meter, it would be more than half
way across his wingspan. So it might be about that much. And obviously, I am just
roughly drawing this, just to give you a sense of
how far a meter might be. And I just wrote
a lowercase m here as really just a short
way of writing meter. So you could imagine
that the smaller things you might want to
measure with the meter are things like a human
being-- a human being's height or a human
being's wingspan. If you wanted to say, well, what
are some of the larger things that you would want to
measure with a meter, you might imagine something
like the height of a skyscraper. So this right over here is
the Empire State Building, at one time the tallest
building in the world, now just a tall building in the world. And this is 443 meters tall. So this is starting to be on
the larger scale of things that you would want to
measure with a meter. Now you're probably
asking, well, what happens if I
want to measure things that are even larger than that? Well the metric
system provides us prefixes to essentially
say multiples of meters. And the unit of distance that
is larger than the meter that is most typically
used is the kilometer. I've heard a few people say
"kill-O-meter," but kilometer, I'll pronounce is
"kuh-LAW-me-ter," which is equivalent
to 1,000 meters. And so when you're
thinking about kilometers, this is thinking about the
distance within a city. This would be even the distance
from one city to another city. Even the radius of the planet
is often measured in kilometers. And to once again get a sense
of that, this right over here is a map of New York City. And right over here
they give us the scale. This distance right over
here is 5 kilometers. So 5 kilometers just to
give us a sense of things-- and they wrote km
for short so 5 km. This lowercase k, lowercase m is
just shorthand for kilometers, this would be equal to-- well
if 1 kilometer is 1,000 meters, 5 kilometers is going
to be 5 times as many. It's going to be 5,000 meters is
this distance right over here. If you were to try to
imagine 1 kilometer, it would be 1/5 of that. So 1 kilometer on this map
might look something like that. Now there's other units
in the metric system that allow us to describe distances
less than a kilometer but more than a meter. But they're not
as typically used. But I'll list them here, just
so that you see that they exist. You have the "hect-O-meter,"
or "heck-TOM-eter"-- it's so infrequently used that
I really haven't heard a lot of people say it-- which
is equal to 100 meters. And you have the "DECK-a-meter"
or "deck-AM-eter," and I actually think
it's "DECK-a-meter." Dekameter, which is 10 meters. And I'm going to
write these in orange because they're not
that frequently used. For example, it's
not typical to hear someone say that the Empire
State Building is 4.43 hectometers or for them to say
that this is 44.3 dekameters. They would typically say
that this is 443 meters. Now you're probably saying,
OK, well, this is fine. Using these prefixes
on the meter, I'm able to describe
distances that are larger than a meter,
that are multiples of tens of the meter
or a multiple of 100 or a multiple of
1,000 of the meter. But what if I want
to go smaller? Well, the metric system
has units for that. And if we go just
1/10 of a meter, this is not used as
typically, but I'll write it here-- the decimeter. The decimeter is
1/10 of a meter. Or another way of
saying it is 1 meter is equal to 10 decimeters,
lowercase dm for short. Once again, this is
not so typically used. But if we go one
scale even below that, we get to the centimeter,
which is a heavily used unit. And here, the prefix
centi means 1/100. So this is 1/100 of a meter. Another way of thinking
about it-- 1 meter is equal to 100 centimeters. And if you wanted to imagine
the scale of a centimeter, you could imagine this
frog right over here on this person's hand might
be several centimeters long. So a centimeter on this drawing
might be around that distance. Now if you want to measure
things even smaller than that, we have another
fairly common unit, and that is the millimeter. And the prefix milli
here refers to 1/1,000. So it's 1/1,000 of a meter. Or another way of thinking
about it is 1 meter is equal to 1,000 millimeter. Actually, let me just
write m for short, just so we used to also
seeing it that way. 1 meter is equal to
1,000 millimeters. And if you wanted
to imagine how long or how far a millimeter
is, you could go down the scale of things that are
smaller than a centimeter. So these ants,
for example, might be 3 or 4 millimeters long. So a millimeter in this
drawing right over here might be something like that. The important thing to realize
or just to conceptualize is you might want to use
different units depending on the scale that
you're measuring. And it's also useful
to just realize what these typical prefixes
refer to because we're seeing it used in distance here. They're all based on the
base unit of distance. But when we're measuring volume
or we're measuring other things in the metric system, these
same prefixes also show up. So you see here when
we're measuring distance, kilo refers to 1,000. A kilometer is
literally 1,000 meters. Hecto refers to 100. A hectometer-- 100 meters. Deka refers to 10. Deci refers to 1/10. So decimeter, literally
1/10 of a meter. Centimeter-- 1/100,
1/100 of a meter. Milli refers to 1/1,000.