—
Mr. Andersen surveys properties of matter. A brief discussion of Archimede’s Principle, Charles Law, Boyle’s Law, and viscosity is included.
—
—
Transcript Provided by YouTube:
00:04
Hi. This is Mr. Andersen. Today I’m going to talk about the properties of
00:08
matter. What is matter? Matter is anything that has mass and takes up space. But in this
00:14
podcast we’re going to talk about large scale measurements of matter. So how large could
00:20
we get? Large enough, if we talk about this. This is actually, if we were to look up in
00:24
the constellation Pegasus, we’d find this. This is a binary system where we have this
00:29
star, which in relation to our sun is much bigger. It’s called IK Pegasi B. And then
00:34
we have this tiny little thing which is a white dwarf. And what is a white dwarf? It’s
00:38
essentially a star that’s lost enough of its mass or lost enough of its energy to kind
00:45
of go dark. The cool thing about white dwarfs, they have always fascinated me, is they have
00:49
a huge amount of density. In other words if we were to look at this one white dwarf right
00:54
here, it has about 1 times 10 to the 6th grams per cubic centimeter for density. What does
01:03
that mean? One cubic centimeter of this would have the mass of 1000 kilograms. So a tiny
01:09
little bit like that would weigh 1000 kilograms. So that’s pretty amazing. Eventually this
01:14
will go red giant. This stuff will go into here and could explode as a supernova. But
01:18
I’m getting ahead of myself. So first of all let’s talk about what density is. Density
01:23
is essentially mass per unit area. And so I like this because it’s a quick way to remember
01:30
density. I’ve got M D V here on the bottom. And so let’s say we had a cube of water that
01:35
looked like this. And that cube of water was 1 centimeter by a centimeter by a centimeter.
01:44
So it’s 1 cubic centimeter. The mass of that would be, we’ll say 1.00 grams. The volume
01:52
would be 1.00 centimeters cubed. And so it would have a density of, well let me stop
01:58
for a second. Because you can use this pyramid. And so what you do is you simply put your
02:02
finger and start at the one that you want to find. And so in this case if I cross out
02:06
density, this tells me that the density it simply the mass divided by the volume. And
02:12
so if I take the mass, which is one. Divide it by the volume, which is one, it’s going
02:16
to give me a density of 1, let me scratch that. Get the significant digits right. 1.00
02:23
grams per cubic centimeter. Okay. So another thing you could do is let’s say, I’m given
02:29
the density but I want to find the mass. That mass is simply going to be the density times
02:35
the volume. Or scratch that. If we want to find the volume, I cover that up. And that’s
02:40
going to be mass divided by the density. So that’s pretty cool. What do we know about
02:44
water? Water is something that’s really weird. And so if I were to have that same cube of
02:48
water and put it in an ice cube tray, it would actually increase the volume. So the volume
02:53
would be greater than one. And that’s because ice actually has a density of 0.92 grams per
02:59
cubic centimeter. That’s why ice floats. But we’ll talk more about why it actually does
03:03
that later. So now we’re presented with the idea of Archimedes. Archimedes had this dilemma.
03:08
The king told him that he wanted him to figure out if the crown that he asked the craftsman
03:15
to make was actually made of gold. Or if the person had actually slipped in some silver
03:20
to save himself some money. And so the story goes that Archimedes thought about this for
03:23
a long period of time. And then eventually he’s taking a bath and he realizes the right
03:29
answer and how to solve it. And he jumps out of the bath and runs through the streets saying
03:33
“Eureka!” In other words “I’ve discovered it.” And so what did he discover? It’s a pretty
03:38
cool idea. He discovered Archimedes Principle. And so Archimedes Principle goes like this.
03:43
What he discovered or his idea is that he could have a balance where on one side of
03:47
that balance he puts the crown. So let’s put the crown like this. And then on the other
03:52
side of the balance he puts a weight of the correct amount of gold. And then he just kind
03:58
of balances this whole thing in water. And so what he could look at is the buoyant force.
04:03
In other words, in a perfect world the buoyant force of the gold and the buoyant force of
04:08
the crown will be the same. But if it’s somehow unequal, then he knows that the guy is trying
04:12
to cheat the king. Okay. So what is buoyancy? Buoyancy is simply is, a way to think about
04:17
it is it’s a fluid that that you’re immersing something in saying, I don’t want this. I’m
04:21
trying to throw it out. And so an example, this right here, this oil tanker is made of
04:27
steel. And steel is going to sink. We know that. And so how is this oil tanker able to
04:32
float? Well that oil tanker is displacing water. And by displacing the water the water
04:39
is exerting a force on that we call the buoyant force up. And so this is a little bit better
04:43
job than that. When you put an object in water, there’s a force of gravity pushing it down.
04:48
But there’s also a buoyant force equal to the weight of the fluid you displace. And
04:54
so by making the volume bigger. In other words decreasing the density, we could make something
05:00
float that normally wouldn’t. So that’s buoyancy. Buoyancy and gases works a little bit differently.
05:07
Buoyancy of gases is a direct relationship. And now we have one of our first laws that
05:11
you should remember. This is Charles Law. Charles Law says this. That as you increase
05:16
the temperature, there’s going to be a direct relationship with the volume. And so if we
05:22
look at this apparatus over here, if I were to somehow crank up the temperature in here,
05:26
that’s going to make the molecules move around more quickly. And that’s going to increase
05:30
the volume. And so an example of this, this is my friend Scott Taylor. He’s go a balloon
05:35
in town. And as he heats up this balloon he increases the volume of it which decreases
05:41
the density. And that makes it float. If he wants to come down when he’s done with the
05:46
balloon trip, all he does is quit firing that propane tank into it. And that’s going to
05:51
decrease the volume and thereby decrease the density. And so it’s going to sink. So Charles
05:56
Law there is a direct relationship between volume and temperature. Next thing I should
06:00
explain is what’s called pressure. Pressure, think about it like this. Inside an object
06:05
pressure is the force of all those molecules pushing out on it. And so the SI unit for
06:11
that, in other words in science we measure that in something called a pascal which is
06:16
named after this guy Blaise Pascal. What is it? It is the force of one newton. And a newton,
06:23
the way I always like to remember a newton, a newton is like the weight of one apple.
06:28
The weight of one apple on one meter cubed. And so a newton is not very big. So normally
06:34
we measure instead of pascals we measure in kilopascals. Which is going to be 1,000 pascals.
06:40
And so the best barometer or the most simple barometer, all you do is in a tank you put
06:45
some mercury. And that mercury goes up a tube like this. And so as the, let me change color
06:51
for just a second, as the air pressure pushes down on it, it pushes that mercury up in the
06:58
tube. And so it’s a way to measure air pressure. And air pressure is incredibly intense. We
07:03
don’t normally notice it. And that’s because we just are surrounded by it. But imagine
07:08
if we go deep down in the ocean, that pressure is big enough that it can actually crush us.
07:13
So that’s pressure. But it finally brings us to what’s called Boyle’s Law. And Boyle’s
07:17
Law says this. If we’ve got pressure and volume, we’ll say right here. And we increase the
07:23
volume. So we’re going to increase the volume of that object. What happens to the pressure?
07:28
The pressure is actually going to decrease. Or a better way to think of it. If we have
07:32
all of this gas, it’s got a really big volume. But we were to somehow squeeze it into this
07:37
little aerosol canister, which has a smaller volume, then it’s going to have a way greater
07:42
pressure. And so it’s going to exert that pressure out. So Boyle’s Law looks like this.
07:47
In other words, as we increase the volume we’re going to decrease the pressure. Likewise,
07:54
if we have a given amount and we decrease the volume, then we’re going to increase that
07:58
pressure. And so these are simple ones that you can actually solve some quick equations
08:04
if you know Boyle’s Law. The 1 and the 2 represent the pressure and the volume initially and
08:10
then after something happens. Okay. Last thing I want to talk about is called viscosity.
08:17
Viscosity is resistance to flow. And so resistance to flow in a material. In other words something
08:22
that has a really high viscosity would be silly putty. Something that has a really low
08:27
viscosity is going to be water. In other words it easily pours. Something that has a viscosity
08:32
somewhere in the middle is going to be honey. I love this picture right here. What they’ve
08:36
done is they’ve actually taken some silly putty. And if you put that silly putty on
08:41
a table with a small hole in it, it will eventually, since it has really high viscosity, will flow
08:46
through here. And so you get kind of this drooping thing coming through it. One interesting
08:51
thing I learned when I was growing up is that windows, the glass that we used to put in
08:56
windows is a really, the glass is actually a liquid. It’s a really high viscosity liquid.
09:02
And so if you go to old windows in old houses you’ll find that they’re actually thicker
09:06
at the bottom. And that’s because the glass is actually slowly oozing down to the bottom.
09:11
And so those are some of the properties of matter. Big things we talked about again is
09:15
Archimedes Principle and buoyancy. But also Charles Law and Boyle’s Law. And so hopefully
09:21
that’s helpful.
—
This post was previously published on YouTube.
—
Photo credit: Screenshot from video.