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## Geometry (all content)

### Course: Geometry (all content) > Unit 8

Lesson 1: Volume of rectangular prisms- Volume intro
- Measuring volume with unit cubes
- Volume of rectangular prisms with unit cubes
- Measuring volume as area times length
- Volume of a rectangular prism
- Volume of rectangular prisms
- Volume of triangular prism & cube
- Volume formula intuition
- Volume of rectangular prisms review
- Conversion between metric units

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# Volume intro

Finding volume, length, and area all involve measuring dimensions in order to quantify a certain aspect of an object or space. Although each property requires different calculations, they all rely on the same fundamental principle: taking measurements and using those measurements to derive a numerical value. When finding volume, you are measuring the amount of space that an object occupies. Created by Sal Khan.

## Want to join the conversation?

- What is the difference between capacity and volume?(52 votes)
- Volume is the amount of space taken up by an object, while capacity is the measure of an object's ability to hold a substance, like a solid, a liquid or a gas. ... Volume is measured in cubic units, while capacity can be measured in almost every other unit, including liters, gallons, pounds, etc.(86 votes)

- How do you calculate the volume of an irregular shape?(12 votes)
- You can calculate the volume of an
**irregular shape**- it just takes a few more steps:

First,**break**the irregular shape into smaller, regular shapes. (*You should know how to calculate the volume of each of these smaller shapes.*)

Next - one at a time -**calculate**the volume of each of the smaller shapes.

Finally,**add up**the volumes of all the smaller shapes. This gives you the total volume of the irregular shape.

Hope this helps!(39 votes)

- heyy yall do yall lke chicken nuggets upvote if yall do! yum dont forget to leave a com(17 votes)
- i do this is the best comment i have heard in a while thanks that made me laugh okay bye i hop you comment back(0 votes)

- a 4-d is when a figure is 3-d holographic(7 votes)
- Human beings are literally incapable of seeing a 4D shape in its most true form. Consider:

If I had a sphere and we could only see in 2D, we'd just see a circle, not the whole sphere.

It's the same idea with 4D VS 3D.(14 votes)

- how do you calculate the volume of an irregular shape?

From,

Charlotte :D(9 votes)- Break the irregular shape into smaller shapes, then calculate the volumes of those. When you are done, add all the volumes together to find the total volume(0 votes)

- In math, volume is the amount of space in a certain 3D object. For instance, a fish tank has 3 feet in length, 1 foot in width and two feet in height. To find the volume, you multiply length times width times height, which is 3x1x2, which equals six. So the volume of the fish tank is 6 cubic feet. Volume is also how loud a sound is. Look on your TV remote. There is a volume control button on it.(20 votes)

- How did human beings find out one line is longer than the other?(6 votes)
- they Measure(5 votes)

- why do we have to watch the videos?(2 votes)
- because are teachers force us:3(9 votes)

- Is it okay if i am going ahead of my grade(6 votes)
- of course! that helps you understand more I know my mom would have me do stuff ahead of my grade just as long as you can balance out the grade your in and not have a breakdown also tip try not to accidentally mix up what your already learning about and what your learning about in the grade ahead... things can get... interesting😬🤫(1 vote)

- Um.... I like chicken nuggets(6 votes)

## Video transcript

Human beings have
always realized that certain things are
longer than other things. For example, this
line segment looks longer than this line segment. But that's not so satisfying
just to make that comparison. You want to be
able to measure it. You want to be able to
quantify how much longer the second one is
than the first one. And how do we go
about doing that? Well, we define a unit length. So if we make this
our unit length, we say this is one unit, then
we could say how many of those the lengths are
each of these lines? So this first line
looks like it is-- we could do one of those units
and then we could do it again, so it looks like
this is two units. While this third one looks
like we can get-- let's see that's 1, 2, 3 of the units. So this is three of the units. And right here, I'm
just saying units. Sometimes we've made conventions
to define a centimeter, where the unit might look
something like this. And it's going to look different
depending on your screen. Or we might have an inch that
looks something like this. Or we might have a
foot that I won't be able to fit on this screen
based on how big I've just drawn the inch or a meter. So there's different
units that you could use to
measure in terms of. But now let's think
about more dimensions. This is literally a
one-dimensional case. This is 1D. Why is it one dimension? Well, I can only measure length. But now let's go to a 2D case. Let's go to two
dimensions where objects could have a length and a
width or a width and a height. So let's imagine two figures
here that look like this. So let's say this
is one of them. This is one of them. And notice, it has a
width and it has a height. Or you could view it as
a width and the length, depending on how
you want to view it. So let's say this is one
figure right over here. And let's say this
is the other one. So this is the other
one right over here. Try to draw them
reasonably well. Now, once again, now
we're in two dimensions. And we want to say, well,
how much in two dimensions space is this taking up? Or how much area are each
of these two taking up? Well, once again, we could
just make a comparison. This second, if you viewed
them as carpets or rectangles, the second rectangle is
taking up more of my screen than this first one, but I
want to be able to measure it. So how would we measure it? Well, once again, we would
define a unit square. Instead of just a unit length,
we now have two dimensions. We have to define a unit square. And so we might make
our unit square. And the unit square we will
define as being a square, where its width
and its height are both equal to the unit length. So this is its width is one
unit and its height is one unit. And so we will often
call this 1 square unit. Oftentimes, you'll
say this is 1 unit. And you put this 2 up here, this
literally means 1 unit squared. And instead of
writing unit, this could've been a centimeter. So this would be 1
square centimeter. But now we can use this
to measure these areas. And just as we said
how many of this unit length could fit
on these lines, we could say, how many of these
unit squares can fit in here? And so here, we might take
one of our unit squares and say, OK, it fills
up that much space. Well, we need more
to cover all of it. Well, there, we'll put
another unit square there. We'll put another unit
square right over there. We'll put another unit
square right over there. Wow, 4 units squares
exactly cover this. So we would say that
this has an area of 4 square units
or 4 units squared. Now what about this
one right over here? Well, here, let's seem I could
fit 1, 2, 3, 4, 5, 6, 7, 8, and 9. So here I could fit 9
units, 9 units squared. Let's keep going. We live in a
three-dimensional world. Why restrict ourselves
to only one or two? So let's go to the 3D case. And once again,
when people say 3D, they're talking
about 3 dimensions. They're talking about
the different directions that you can measure things in. Here there's only length. Here there is length and
width or width and height. And here, there'll be
width and height and depth. So once again, if you have,
let's say, an object, and now we're in three dimensions,
we're in the world we live in that looks
like this, and then you have another object
that looks like this, it looks like this second
object takes up more space, more physical space than
this first object does. It looks like it
has a larger volume. But how do we
actually measure that? And remember, volume is just how
much space something takes up in three dimensions. Area is how much space something
takes up in two dimensions. Length is how much
space something takes up in one dimension. But when we think
about space, we're normally thinking
about three dimensions. So how much space would
you take up in the world that we live in? So just like we did before,
we can define, instead of a unit length
or unit area, we can define a unit
volume or unit cube. So let's do that. Let's define our unit cube. And here, it's a cube so its
length, width, and height are going to be the same value. So my best attempt
at drawing a cube. And they're all
going to be one unit. So it's going to be one
unit high, one unit deep, and one unit wide. And so to measure volume,
we could say, well, how many of these
unit cubes can fit into these different shapes? Well, this one right
over here, and you won't be able to
actually see all of them. I could essentially
break it down into-- so let me see
how well I can do this so that we can count them all. It's a little bit
harder to see them all because there's some
cubes that are behind us. But if you think of
it as two layers, so one layer would
look like this. One layer is going
to look like this. So imagine two things like this
stacked on top of each other. So this one's going to
have 1, 2, 3, 4 cubes. Now, this is going
to have two of these stacked on top of each other. So here you have 8 unit cubes. Or you could have 8
units cubed volume. What about here? If we try to fit
it all in-- let me see how well I could draw this. It's going to look
something like this. And obviously, this is
kind of a rough drawing. And so if we were to
try to take this apart, you would essentially have a
stack of three sections that would each look
something like this. My best attempt at drawing it. Three sections that
would look something like what I'm about to draw. So it would look like this. So if you took three of
these and stacked them on top of each other, you'd
get this right over here. And each of these have 1, 2, 3,
4, 5, 6, 7, 8, 9 cubes in it. 9 times 3, you're going to
have 27 cubic units in this one right over here. So hopefully that helps
us think a little bit about how we measure
things especially how we measure things in
different number of dimensions, especially in three dimensions
when we call it volume.