Metric units for weight

Let's think about the
units typically used

in the metric system to
measure an object's weight.

And I'm putting the
weight in quotation marks

right over here because the
units I'm going to talk about

are-- actually, if we
wanted to be technical,

they're units of mass.

And as we'll see later on
in our scientific careers,

that weight and mass
are not the same thing.

They are related.

Mass you could view as
how much stuff there is.

How much substance
does an object have?

How hard is it to change
the velocity of an object?

While weight is,
what's the force

that gravity is pulling
down on that object?

Now, in everyday
life, if we're just

on the same planet or the
same part of the planet,

if something has more mass,
it's going to have more weight.

And if something
has more weight,

it's going to have more mass.

And that's why in
everyday language

these words are
often interchanged.

Later on, we'll see that
these mean different things.

For the sake of this
video, because we're really

just getting ourselves warmed
up with some of these units,

I will use these
interchangeably.

I'll use them in kind of
the everyday language sense,

not in the technical
physics sense of the word.

So in the metric
system when people

talk about measuring
relatively light things,

they will often use the gram.

And to get a sense of
things that weight a gram,

one example is a paper clip.

Your average size paper clip
would weigh about a gram.

A stick of chewing gum, not even
the whole pack of chewing gum,

just a stick of chewing gum,
would weigh about a gram.

A dollar bill would
weigh about a gram.

So this really isn't
a lot of weight.

Now, if you wanted to measure
things more on, I would say,

a human scale, you
could then increase

by a factor of thousand
and go to the kilogram.

Kilogram.

And as the unit implies, as the
prefix implies I should say,

kilo, a thousand.

This means 1,000 grams.

And if you want to think about
how much that represents,

well, many people will
measure their weight

in terms of kilograms.

So I, for example, weigh
about 70 kilograms.

And I'm 5' 9''.

And I'm about average build
and I weigh about 70 kilograms.

If you want to imagine
what a kilogram is like,

imagine taking a liter of
fluid or a liter of water.

So if you took a liter of water.

And a liter, you could
imagine as a 10 centimeter

deep cube, 10 centimeters
wide, and 10 centimeters high.

If you filled this up with
water, the weight of that thing

is going to be 1 kilogram.

I know you're not
used to walking around

with 1 liter cubes of water.

Another way of
thinking about it,

if you go to the
supermarket and you

were to buy a 2 liter of soda.

And sometimes you buy 2
liters of other things

as well-- water, whatever.

If you buy a 2 liter of soda
is going to weigh-- well,

actually, 2 liters of
water, in particular,

is going to weigh-- soda
has other things in it,

so you can't be as
precise with the weight.

But 2 liters of
water, I should say,

are going to weigh
exactly 2 kilograms.

We're just talking
about the water itself.

We're not talking
about the container.

But if you want to get a rough
sense for how much weight

that is, that's going
to be 2 kilograms.

So if you're measuring
human scale size

things, reasonable size
quantities of fluid,

objects around this
scale, kilogram

makes a lot more sense.

If you measure these
very light things,

you're talking about a gram.

If you want to get
really precise,

this might be more in things
if you're doing a drug dosage

and you need to be very,
very, very precise,

then you will sometimes see
people go to the milligram.

But you could imagine a
milligram is 1/1,000 of a gram.

And so 1/1,000 the weight
of a dollar bill or 1/1,000

the weight of a paper clip,
this is very, very, very,

very small.

So this usually doesn't come
into play in our everyday life.