Properties of Matter
Hi. This is Mr. Andersen. Today
I’m going to talk about the properties of matter. What is matter? Matter is anything
that has mass and takes up space. But in this podcast we’re going to talk about large scale
measurements of matter. So how large could we get? Large enough, if we talk about this.
This is actually, if we were to look up in the constellation Pegasus, we’d find this.
This is a binary system where we have this star, which in relation to our sun is much
bigger. It’s called IK Pegasi B. And then we have this tiny little thing which is a
white dwarf. And what is a white dwarf? It’s essentially a star that’s lost enough of its
mass or lost enough of its energy to kind of go dark. The cool thing about white dwarfs,
they have always fascinated me, is they have a huge amount of density. In other words if
we were to look at this one white dwarf right here, it has about 1 times 10 to the 6th grams
per cubic centimeter for density. What does that mean? One cubic centimeter of this would
have the mass of 1000 kilograms. So a tiny little bit like that would weigh 1000 kilograms.
So that’s pretty amazing. Eventually this will go red giant. This stuff will go into
here and could explode as a supernova. But I’m getting ahead of myself. So first of all
let’s talk about what density is. Density is essentially mass per unit area. And so
I like this because it’s a quick way to remember density. I’ve got M D V here on the bottom.
And so let’s say we had a cube of water that looked like this. And that cube of water was
1 centimeter by a centimeter by a centimeter. So it’s 1 cubic centimeter. The mass of that
would be, we’ll say 1.00 grams. The volume would be 1.00 centimeters cubed. And so it
would have a density of, well let me stop for a second. Because you can use this pyramid.
And so what you do is you simply put your finger and start at the one that you want
to find. And so in this case if I cross out density, this tells me that the density it
simply the mass divided by the volume. And so if I take the mass, which is one. Divide
it by the volume, which is one, it’s going to give me a density of 1, let me scratch
that. Get the significant digits right. 1.00 grams per cubic centimeter. Okay. So another
thing you could do is let’s say, I’m given the density but I want to find the mass. That
mass is simply going to be the density times the volume. Or scratch that. If we want to
find the volume, I cover that up. And that’s going to be mass divided by the density. So
that’s pretty cool. What do we know about water? Water is something that’s really weird.
And so if I were to have that same cube of water and put it in an ice cube tray, it would
actually increase the volume. So the volume would be greater than one. And that’s because
ice actually has a density of 0.92 grams per cubic centimeter. That’s why ice floats. But
we’ll talk more about why it actually does that later. So now we’re presented with the
idea of Archimedes. Archimedes had this dilemma. The king told him that he wanted him to figure
out if the crown that he asked the craftsman to make was actually made of gold. Or if the
person had actually slipped in some silver to save himself some money. And so the story
goes that Archimedes thought about this for a long period of time. And then eventually
he’s taking a bath and he realizes the right answer and how to solve it. And he jumps out
of the bath and runs through the streets saying “Eureka!” In other words “I’ve discovered
it.” And so what did he discover? It’s a pretty cool idea. He discovered Archimedes Principle.
And so Archimedes Principle goes like this. What he discovered or his idea is that he
could have a balance where on one side of that balance he puts the crown. So let’s put
the crown like this. And then on the other side of the balance he puts a weight of the
correct amount of gold. And then he just kind of balances this whole thing in water. And
so what he could look at is the buoyant force. In other words, in a perfect world the buoyant
force of the gold and the buoyant force of the crown will be the same. But if it’s somehow
unequal, then he knows that the guy is trying to cheat the king. Okay. So what is buoyancy?
Buoyancy is simply is, a way to think about it is it’s a fluid that that you’re immersing
something in saying, I don’t want this. I’m trying to throw it out. And so an example,
this right here, this oil tanker is made of steel. And steel is going to sink. We know
that. And so how is this oil tanker able to float? Well that oil tanker is displacing
water. And by displacing the water the water is exerting a force on that we call the buoyant
force up. And so this is a little bit better job than that. When you put an object in water,
there’s a force of gravity pushing it down. But there’s also a buoyant force equal to
the weight of the fluid you displace. And so by making the volume bigger. In other words
decreasing the density, we could make something float that normally wouldn’t. So that’s buoyancy.
Buoyancy and gases works a little bit differently. Buoyancy of gases is a direct relationship.
And now we have one of our first laws that you should remember. This is Charles Law.
Charles Law says this. That as you increase the temperature, there’s going to be a direct
relationship with the volume. And so if we look at this apparatus over here, if I were
to somehow crank up the temperature in here, that’s going to make the molecules move around
more quickly. And that’s going to increase the volume. And so an example of this, this
is my friend Scott Taylor. He’s go a balloon in town. And as he heats up this balloon he
increases the volume of it which decreases the density. And that makes it float. If he
wants to come down when he’s done with the balloon trip, all he does is quit firing that
propane tank into it. And that’s going to decrease the volume and thereby decrease the
density. And so it’s going to sink. So Charles Law there is a direct relationship between
volume and temperature. Next thing I should explain is what’s called pressure. Pressure,
think about it like this. Inside an object pressure is the force of all those molecules
pushing out on it. And so the SI unit for that, in other words in science we measure
that in something called a pascal which is named after this guy Blaise Pascal. What is
it? It is the force of one newton. And a newton, the way I always like to remember a newton,
a newton is like the weight of one apple. The weight of one apple on one meter cubed.
And so a newton is not very big. So normally we measure instead of pascals we measure in
kilopascals. Which is going to be 1,000 pascals. And so the best barometer or the most simple
barometer, all you do is in a tank you put some mercury. And that mercury goes up a tube
like this. And so as the, let me change color for just a second, as the air pressure pushes
down on it, it pushes that mercury up in the tube. And so it’s a way to measure air pressure.
And air pressure is incredibly intense. We don’t normally notice it. And that’s because
we just are surrounded by it. But imagine if we go deep down in the ocean, that pressure
is big enough that it can actually crush us. So that’s pressure. But it finally brings
us to what’s called Boyle’s Law. And Boyle’s Law says this. If we’ve got pressure and volume,
we’ll say right here. And we increase the volume. So we’re going to increase the volume
of that object. What happens to the pressure? The pressure is actually going to decrease.
Or a better way to think of it. If we have all of this gas, it’s got a really big volume.
But we were to somehow squeeze it into this little aerosol canister, which has a smaller
volume, then it’s going to have a way greater pressure. And so it’s going to exert that
pressure out. So Boyle’s Law looks like this. In other words, as we increase the volume
we’re going to decrease the pressure. Likewise, if we have a given amount and we decrease
the volume, then we’re going to increase that pressure. And so these are simple ones that
you can actually solve some quick equations if you know Boyle’s Law. The 1 and the 2 represent
the pressure and the volume initially and then after something happens. Okay. Last thing
I want to talk about is called viscosity. Viscosity is resistance to flow. And so resistance
to flow in a material. In other words something that has a really high viscosity would be
silly putty. Something that has a really low viscosity is going to be water. In other words
it easily pours. Something that has a viscosity somewhere in the middle is going to be honey.
I love this picture right here. What they’ve done is they’ve actually taken some silly
putty. And if you put that silly putty on a table with a small hole in it, it will eventually,
since it has really high viscosity, will flow through here. And so you get kind of this
drooping thing coming through it. One interesting thing I learned when I was growing up is that
windows, the glass that we used to put in windows is a really, the glass is actually
a liquid. It’s a really high viscosity liquid. And so if you go to old windows in old houses
you’ll find that they’re actually thicker at the bottom. And that’s because the glass
is actually slowly oozing down to the bottom. And so those are some of the properties of
matter. Big things we talked about again is Archimedes Principle and buoyancy. But also
Charles Law and Boyle’s Law. And so hopefully that’s helpful.