Hi. It's Paul Andersen and this
is Crosscutting Concept 5. It's on Energy
and Matter and how energy and matter flow
through a system, how they're recycled and
how they're conserved over time. And so our
earth constantly gets energy from the sun
and a lot of that eventually becomes heat.
But a lot of the things are recycled on the
planet. A lot of the matter like water is
recycled. In other words, it's used over and
over and over again. And so it's important
that our students understand how energy and
matter work because in science it allows us
to properly study and understand systems.
And systems are super important in engineering
because it allows us to control the system
and therefore improve the design. And so what
is a system? Remember that's separate from
the universe. It's a part of the universe
that we choose to study. And it could be as
simple as a green house or machine. Your brain
could be a system. And even the whole could
be a system. And so basically it's something
separate from the universe. And so if we have
a system it can be acted on by forces outside
the system. But since we're talking about
matter and energy, that matter and energy
has to get in to the system and then a lot
of the time it has to get back out of the
system as well. And so we need input and we
need output in order for matter and energy
to be used by a system. And so what is flow?
Flow is essentially matter or energy moving
into a system, moving through the system and
then moving out again. And what is a cycle?
A cycle is when matter or energy are recycled
over and over again within a system. Now one
concept that you want to make sure your students
understand is the idea of conservation of
mass. And conservation of energy. In other
words, the amount of energy that goes into
a system is going to equal the amount of energy
that comes out. The amount of matter or mass
that goes into a system is going to equal
the amount that comes out. And so this idea
of conservation is super important and totally
true. One little caveat to that remember is
that we can convert matter into energy. But
that rarely happens. And we're not going to
see it until the end of this slide show. And
so let me give you a real example of this.
So energy flow. You're probably familiar with
the greenhouse effect. And so what is the
greenhouse effect? Basically since we have
an atmosphere, energy that comes in, so solar
energy, instead of just being reflected back
out into space, some of that is converted
into infrared radiation. Some of that's converted
into heat. And so if we look on this chart
there are 343 watts per meter squared of energy
that's coming from the sun. And a lot of that
is just going to be reflected back out, either
at the top or in the middle of our atmosphere.
Or even off the surface of the planet. And
so that makes up about 103 watts per meter
squared that's being bounced right back into
space. What happens to the rest of the energy?
Well that's going to hit the planet. It's
going to be absorbed by the planet and it's
going to be converted into something called
radiation or infrared radiation or heat. A
lot of it's going to hit greenhouse gases
and get bounced back again to the earth. And
so basically the energy doesn't stay here,
the energy is eventually going to leave as
heat but we're converting more of that visible
light into heat and that keeps our climate
really, really warm. So for example, Mercury,
even though it's much closer to the sun, is
going to be really, really cold because they
don't have an atmosphere that can do this.
But if you look at these numbers, it's going
to be exactly equal to the amount of energy
that we're losing that we gain. It's just
that it's converted into heat. If we look
at cycling, how does that work? Well one cycle
that you're probably familiar with is the
water cycle. In other words the water on our
planet is constant. The water that we have
in our oceans and lakes and in the clouds
and in the ground water is the same. In other
words we have a set amount of matter and so
it's recycled on our planet. Sometimes it's
in the clouds. Sometimes it's in rain. Sometimes
it's in runoff. Sometime's it's in the ocean.
And sometimes it evaporates back into the
clouds again or moves through plants through
evapotransporation. But the amount that we
have is the same. When you have a glass of
water, that water, the molecules in it used
to be in an ocean along time ago. It used
to be in a cloud and it used to be in rain.
It's just recycled over and over and over
again. But the amount we have is conserved
or it stays the same. Why is it important
in engineering? Well think about it. Let's
say you're trying to design a solar powered
car. It's important that you understand how
much energy is coming in and how we convert
that to other forms of energy. We can store
some of that energy in a battery. And we can
utilize some of that energy using electric
motors. And so there are some misconceptions
that I want to talk about in relation to matter
and energy. And they're just going to jump
up and it's important that we address these.
And so here's something that's interesting.
When you go to bed at night and you wake up
in the morning, if you were to weigh yourself
you would find that you're going to weigh
about half a pound less in the morning. In
other words you loose weight at night. And
if I were to ask you where it went a really
common response I get from students is that
you burn it up as energy. Now know this. We
can't convert matter into energy. It happens
very rarely and again we're only going to
talk about it when we get to the end of this
video. And so where does it go? Well the matter
is released. You're breathing it out as carbon
dioxide and water vapor and so you're losing
matter from your food there, but we're using
some of the energy that was found in the bonds
of that food that we have. And that's what
we're using to keep our heart beating, keep
our body alive. Here's some other misconceptions.
When you say you're drinking an energy drink
or you have an energy bar, there's this idea
that there's some secret energy that's found
within it. And that's not true. The energy
is going to be found in the chemical bonds
of the food and we can release some of that
energy and convert it into another form, but
it doesn't have some certain kind of energy
in it. And how do we do weight gain? In other
words, where does a tree get all of it's mass?
If you were to ask that question to students
they would say, maybe the mass comes in from
it's roots and water. Maybe it's minerals
coming into the roots. But they don't see
where the matter is going into the tree. The
matter is coming into the tree in carbon dioxide.
So that matter is moving in through it's leaves
and then it's using that carbon dioxide to
make the wood. And eventually we can lose
that again. And so there's some real weird
misconceptions about energy and matter and
that's important when we think about the progression
of which we're going to teach this. And so
we want our students to understand how matter
and energy interact with one another. But
it's important that we don't talk about energy
right away. In the lower elementary grades
we should just be talking about matter and
how matter can flow and how matter can cycle.
We shouldn't talk about energy until we get
to middle school and then we should be really
careful about how we talk about energy and
making sure we're using the right terms. And
then finally we get into conservation. There's
a lot of cool labs you can do so you can study
how matter is conserved and even energy is
conserved as well. And so where do you start?
What's the progression? In other words how
do you start in the lower elementary grades
and work you're way up into high school? How
do you get your students studying matter and
energy? In other words, throwing darts at
the dart board, but getting better and better
over time? Well you should start with matter.
And it's really understandable to students
what liquids, solid and gas is. And so you
can deal with forms of matter and what matter
is and what it's made up of. You could start
with that at the elementary grade. At least
different forms of matter. That's pretty straight
forward. As you move through elementary then
you should bring forward these ideas of matter
flow and then matter cycling. But we shouldn't
really talk about energy yet. We'll save that
until they get to middle school and high school.
And so what's an example? Well this plant
right here is taking in matter from it's roots.
It's taking in water for example. That water
is going to move through the plant and then
it's eventually going to evaporate off of
the leaves. If we were to put a bag over that
plant we're going to collect a lot of water
vapor inside it. And so we could study how
water is flowing through it, but we could
also study how other matter is used. And one
that is really misunderstood is the carbon
cycle. And so I would talk about the carbon
cycle if it were me. Carbon remember is mostly
going to sit in the atmosphere as carbon dioxide
and where is it going to go? Well it's going
to be used by plants. Plants are going to
take it in through their leaves. They do photosynthesis.
And they use that to make the plant. Eventually
we're going to release that because we're
going to eat plants or things that eat plants
and then we're going to release that carbon
in that food as carbon dioxide. It goes back
into the atmosphere again. And so that's a
great thing to talk about. The amount of carbon
we have on our planet is the same. It's just
going to be recycled over and over. As we
move into middle school then we can really
start to talk about energy. And so a good
place to start is talking about metabolism.
And so our food contains energy. It contains
free energy that we can use to do things.
And so how does that work? Well you're taking
in food, carbohydrates, fats, things like
that. And then it's eventually going to leave
you. In other words, the amount of matter
that we take in and the amount of matter that
we're giving off is going to be exactly the
same. In other words we have to account for
all of that matter that comes in and goes
out. So what happens to the energy? Well in
cellular respiration we can release some of
that potential energy that's found in our
food and we can release that during metabolism
and we usually convert it into something called
ATP. But we're not somehow creating energy
in the food. Or it doesn't have energy. You
probably want to address the difference between
mass and weight at this point as well. And
so mass remember is a measure of the amount
of matter that we have but weight is going
to be the gravitational attraction. In other
words how much the earth is pulling on us.
And so mass and weight are going to be the
same if you are on our planet but if you were
to move to the moon you're mass stays the
same, but you're weight is going to change
because the gravity is going to change. And
so a way to think about that, this hot air
balloon, if you were to put it on a scale,
since it's buoyant, it's not going to weigh
anything, but that doesn't mean that it doesn't
have matter, it doesn't have mass, it doesn't
have inertia. We can study this in the lab
as well as we move into high school. We can
look at the conservation of matter. And so
a really simple experiment is to take a given
amount of water and we could mass that, get
it's mass, we could take a given amount of
sugar and then we could add the sugar to the
water, dissolve it and then we could measure
their combined mass. And a lot of students
this it's somehow going to increase or decrease.
The sum of those original masses is going
to equal the sum of the sugar water. In other
words we're just changing, we're just dissolving
that sugar in the water. And you could even
do chemical reactions. So a typical one would
be to take water and an Alka Seltzer tablet.
You take the mass of the water and the Alka
Seltzer tablet before you put them together.
You have to be sure since we're going to produce
a gas that you have a bag around this or you
do it in some kind of closed container. But
basically we take the matter before and after
and we're going to have the same amount of
matter or conservation of matter. What's in
Alka Seltzer? It's basically baking soda and
citric acid. And so it's that same old vinegar
and baking soda reaction that you've seen
before. And that would be another thing that
you could do in the lab. And then finally
we're going to get to the nucleus. And so
what is the nucleus? It's at the center of
every atom. It's made up of two different
particles. It's going to have protons. Those
are going to be the red ones here. And then
it's going to have the blue ones which are
neutrons. And so these together are called
nucleons or both of those. It just means that
they inhabit the nucleus. And one thing that
should make you think a little bit when you're
thinking about the nucleus is that we have
all of these positive charges on the inside
and so you know that positive charges repel
each other. And so how do we get them to stay
in the nucleus? Well there's a force that
many people are not familiar with. It's called
the strong nuclear force. The strong force.
And basically what that means it's a force
that holds these nucleons together and holds
them in the nucleus. You don't sense it because
it only occurs at really close proximity,
but there's something that's holding it together.
And so we can also have what's called a nuclear
reaction. So unlike a chemical reaction, what
we're doing is were combining two nuclei or
one nuclei and then another particle. And
so this is an example of one. We've got lithium.
Lithium is going to have three protons and
three neutrons. And then we have deuterium.
Deuterium is going to have one proton but
it's also going to have a neutron. And so
if we were to put those together at the same
place at the same time, we're going to form
an unstable nuclei and then it's going to
basically decay into alpha particles. And
so we write that like this. We have our lithium
here. It's got three for an atomic number
and a mass number of six. Plus our hydrogen
or our deuterium and basically it's going
to breakdown into these two alpha particles.
Which is really a helium nuclei. What's coming
out of that? Well we're converting mass. In
other words we're changing the mass and as
we do that we're decreasing the amount of
mass and we're releasing energy. And so where
does the energy in a nuclear bomb come from
or a nuclear reactor? We're actually converting
mass into a smaller amount of mass. And even
though it's infinitesimal we're releasing
a huge amount of energy. So that's matter,
that's energy, it's really cool and I hope
that was helpful.
