Hi. It's Paul Andersen and this is cross-cutting concept 7. It's on stability
and change. In other words how things remain the same but how they also become different
over time. And so if I were to say these three books are sitting on a table. Is that stability?
Or is that change? Well that looks pretty stable. But if you were to watch the atoms
in the bottom of the book and that atoms in the table, we'll find that there's going to
be a lot of interaction between the two. There's going to be small indentations in the table.
The book's responding to those. So even something that looks inherently stable is going to change
over time. And if we were to come back in a million years, I promise you the books won't
look the way they do. But if we were to look at the moon and see how the moon changes over
time. How it goes through the phases, we would say well, that's definitely changing over
time. But we would also find stability within that. In other words it's always going through
the same phases every month. And so we can start to see a pattern of stability in the
moon over time. And so understanding these things is important for students because in
science it allows us to see patterns. Explain patterns. And then explain phenomena. And
in engineering we're trying to improve design. And so if we really have an understanding
how a system works and how to control that system, that gives us a greater ability in
engineering. And so remember, what is a system? A system is a portion of the universe that
separate from the universe. And so a system for example could be a reservoir. And a dam
that's holding the water back in the reservoir. It could also be your house or a room in your
house could be a system. But it also could be at the level of a small cell. Like in this
case we have a bacteria cell. Or it could even be at the level of a galaxy. We could
think of that as a system. And so all systems have two features that are going to allow
it to remain the same or change over time. Those are going to be the controls. The controls
allow matter and energy into a system and out. And then the other thing we have, that
we haven't talked about in these concepts yet is the idea of feedback and feedback loops.
So let's say we look at a reservoir. And so a reservoir is going to have controls. Controls
are going to allow water into the dam. And then it's going to allow water pass the dam.
So those are going to be controls on the matter coming in. And it's also inherent, the energy.
But then we have feedback loops within the dam. And so a good dam engineer is going to
set it up so that he can measure the amount of water that's coming in. And if there's
more water, then it can hold then he better let some out. And if there's not enough water,
he better not let any go. And so that would be an example of a feedback loop. Or what
about inside a bacterial cell? Bacterial cell is going to have controls on what material
gets in. So what matter does it require? What energy does it require? But it's going to
have feedback loops within the cell itself so it can maintain stability. And so feedback
loops are very very important. And a great example of this is a speed sign. So let's
say you're driving down the road and you see a speed sign. And it says you can only go
30 miles per hour, but this one says that you're currently going 32. Well we can use
what's called a negative feedback loop to maintain that. So what are you going to do?
You're going to slow down. And as you take your foot off the accelerator, the speed is
going to drop. Now you're going too slow, you're going to start to speed up and so eventually
you can reach a stability. You can reach that stable point of around 30 miles per hour.
So negative feedback loops keep us around a set point. Positive feedback loops are different.
So in a positive feedback loop I'm going to move away from that as quickly as I can. So
if I see 30 miles an hour, I'm like I can go faster than that. I can go 39. I can go
51. I can go 72. I can peg it out moving way away from that speed limit. So that's a positive
feedback loop. If we want to move away from a set point, then we use positive feedback
loops. So let's talk about an example of a negative feedback loop in your house. Well
your thermostat is a great example of that. So if it's cold, you basically are setting
the temperature where you want it to be. So let's set it to 70 degrees. If it's colder
than that, then it's going to turn on a heater. And it's going to get warmer and warmer and
warmer until it gets to over 70 degrees, let's say around 71 degrees and then it turns the
heater off. And then it's going to get cooler and then it's going to turn it on. When it
gets too cold, and then it's going to keep going back and forth. And so it can keep it
around a set point. Now I only have a heater in my classroom. So in the spring when it
gets really, really hot, an air conditioner would be nice as well. And that would be used
if it get's too hot. You could turn the air conditioner on and bring it back to a stable
environment. What's a positive feedback loop? That's when we want to move away from a set
point. So an example in the life sciences, have you ever noticed that all the fruit on
a tree go ripe at the same time? Well the way they do that is they're giving off a gas
called ethylene. That gas is going to diffuse out. It's going to trigger other apples to
give off gas and be come ripe as well. And so now we get a feedback loop where they're
all quickly going ripe at the same time. But that's because we're increasing the amount
of this ethylene. And so one bad apple really can spoil the lot by passing this gas to the
others. And so we're getting at this idea of equilibrium. So equilibrium is when the
internal system tends to stay the same. And it's very important in life science, earth
sciences and physical sciences. And so this bird is maintaining internal equilibrium.
And we tend to call that homeostasis. So it's going to have a stable internal temperature.
It's going to have a stable solute concentration on the inside. And the same thing is going
to occur in this fighter jet right here. It has to maintain equilibrium. And if we fall
outside of that, in a bird we call that death. And so if you can't maintain equilibrium you're
going to die. Or in a plane, if it runs out of gas for example, if we don't have that
control set right, then the plane is going to crash. And so what is our goal in the science
classroom? We want students to understand stability and change. And the progression
should be taught in the following way. In the early elementary we should start to develop
language of stability, change and feedback in our students. As they move into the upper
elementary grades we should understand and explain patterns and how patterns change over
time. As we move into middle school we can really talk about the specifics of the different
types of feedback loops, both positive and negative. And then as we move into high school
we want to understand how very complex systems work. And how they maintain a stable internal
environment. And so how do you teach this? Well you start by giving them the language
of stability change and then sensing patterns. And so a great way to start with this would
be a balancing activity. And so if these were perfectly balanced, what students could play
around with on a simple lever like this, is we can find relationships between the two
sides. So how do we get it to maintain stability? And then what happens if we don't maintain
stability over time? If we're looking at patterns as we move on into the upper elementary grades,
great examples are go look at weather, for example. So the weather is some what stable
during the day. But it's going to change throughout the seasons. And so by measuring the stability
in the changes and making predictions about that, we can start to understand how phenomena
work. Or if we go back to the moon, remember the moon is going to go through phases. And
so if we were to just keep track of that in the classroom, what phase is it in, we can
then use that to start to build a model about how the moon and the phases of the moon work.
And most people don't really understand that. Even a simple animation like this. We could
pause it right here. Let's go back to the beginning. And we could simply go through
it. You can see that here's the date. So this is November 10th. It's going to look like
that. If I go forward to, or I guess that was the 18th. If I go forward to the 20th,
it's going to look like that. If we're going to go forward to the 21st it's going to look
like that. And so we could use this to see how we're getting change within the moon.
And then we could use that to make predictions about how the phases of the moon work. As
we move into middle school, we should understand the importance of maintaining stability on
the inside. And so for us we have a temperature of around 37 degrees celsius inside our body.
So that body temperature is super important to maintain. And we use feedback loops, negative
feedback loops to maintain that. And so talk about that with your students. What happens
if you're temperature gets too warm. What are you going to do? Well we're going to sweat.
That would be one good thing that we're going to do. We're going to start to vasodilator.
So we're going to move blood near the surface of the body to loose that. What happen if
it gets to cold? Then we're going to start to shiver. We're going to start to vasoconstrict.
Our hair is going to stand up on end. And so that's a stable internal system of body
temperature. But that's been selected for. So this spider right here, if we're looking
at it with a heat, this is a thermal imaging camera, you can see that the person holding
it, they're body temperature is going to be around 37 degrees celsius, but if you look
at the spider itself, its body is going to be really, really cold. And so now we've got
an endotherm and an ectotherm. In other words this spider is not maintaining a stable internal
environment. It's what we call cold blooded. But you can see that it's got a really, really
warm abdomen here. And so feedback loops are used to maintain that. And then as we move
on into the high school, we should really understand how stability and change effect
one another. And so computer modeling or mathematical modeling is a great way to get at complex
systems. Like natural selection, So this right here is a net logo simulation. It's looking
at the temperature of peppered moths. And peppered moths remember, in Europe, were really
light in color. And then during they during the industrial revolution they became dark
in color. And then as we started to clean up the pollution, they started to become light
in color. And so this simulation, I'll put a link down below, you can use to measure
how they changed over time. How we actually saw evolution. And you can see a real increase
in the light population from a random start. But then we can see what happens if we change
that environment. And so stability and change are important. We use feedback loops and controls
to maintain those. And I hope that was helpful. }