Global-Warming

My nephew manages the science curriculum at a large summer day camp. We had breakfast the other day, and got to talking about global warming, so I wrote up something that might be appropriate for 8th graders at that camp. I doubt that it'll get used, but I like it, so I'll save it. I expect there are still typos that need fixing. With any luck, I'll get to them.

CONTENTS

Overview - How CO2 and H2O work

Introduction - time, GPS, Electricity

Some Basic Science - Electromagnetic spectrum (emc), Waves, Photons

What's an Atom and a Molecule - structure, periodic table, elements

Distances and Speeds - Light Years

Ideal Gas, Mol, STP

H2O and CO2 - vibration mode, frequency, Energy

The Sun

Temperature of the Earth

Global Warming - Experiments

Results - CO2 absorbs infrared energy, air does not

More - Ozone, 92 elements

OVERVIEW (I'm going to skip around and talk about things I think are important)

This is going to be a talk about global warming, what it is, and how and why it works. The basic idea is that when the sun is shining, you can see the light, although when it's cloudy, it's not as bright. But sunlight passes through air pretty freely - you have a sharp shadow. Through clouds, the light gets 'scattered', and your shadow disappears, because light is coming from all over the sky, not just the sun.

Sunlight heats up the black street outside during the day. At night, the street cools off. If you've walked out in bare feet, you know that. Why does this matter? What happens is that carbon dioxide ( CO2 ) and water ( H2O ) kind of scatter the heat that comes off the road, kind of like clouds scatter sunlight. But they do not scatter visible sunlight. In that 'scattering', some heat is 'reflected' back to the earth, warming it. IF there were no water or CO2 in the atmosphere, the average temperature of the earth would be well below freezing, so global warming makes a huge difference. We're going to talk much more about this, and do a couple experiments, but that's the basic outline of where we're going. We'll start with some basic science, much like you started learning letters before reading, and numbers before doing multiplication. By the end, you'll have a reasonable start on some physics and chemistry that you'll learn in high school. BTW, you really want to take physics, chemistry, and biology, and all the math you can manage, in high school. It will serve you well all your life. So, now to the basics.

INTRODUCTION

First, let's think about how to think about things. Einstein has shown that time slows down, as one goes faster. IF you were able to travel around the earth a few gazillion times, at 99.9% of the speed of light, for what you thought was a day, and then come back to earth, you'd age 1 day. Everybody on earth would be a month or more older, because time went slower for you than for them. If they wanted you to set a timer for them, maybe for 1 hour their time, you'd set your timer to a couple minutes. When your timer went off, you could tell them, and they would see what you saw as 2 minutes, as being an entire hour.

Maybe you use some GPS (global positioning system) device in your car for driving directions. They work because the 24 satellites orbit the earth in very precise orbits, and broadcast the time in their internal clocks, and their position. Your GPS device knows how to use 3 or more such signals to determine where you are, within a few feet. It keeps track of several readings to determine how fast, and which direction you are going, and it shows that on the map you can see. In order for that to work the clock in the satellite must be perfectly accurate, however, depending on speed, time changes. SO, satellite clocks are set on earth to be a bit fast, because, relative to us here on the ground, they are going to slow down.

Why did we talk about that? Because we need to understand that we all think of time the same way, "It's 1 o'clock" which is perfectly okay for us, even though the exact science is a bit off. We just can't see it. We're going to talk about the structure of an atom, and a molecule. The real structure is not the same as we'll talk about, but we talk about it in our way because it makes it easier for us to understand without getting bogged down, for example, in the difference in time depending on speed.

In the same way, when talking about electricity, we often compare it to water in a garden hose. Pressure determines how far it will squirt. How fast it will fill a bucket is the volume. If you watch a fireman's hose, there's more pressure, it squirts farther, but what's most important is the volume - it fills up your bucket almost instantly.

SO, with electricity, there's volts (pressure) and amps (amperes / volume), and Ohms is electrical resistance, kind of like how small the nozzle, that's restricting water flow, is. It's not the same, and we should remember that, however, for our purposes today, it's not bad to think of it that way.

SOME BASIC SCIENCE

https://www.miniphysics.com/wp-content/uploads/2011/07/electromagneticspectrum.jpg

Electromagnetic energy is SORT OF transmitted in waves, very vaguely like you see in an ocean. OR, if you stretch a clothes line, fastened at each end, you can tweak it at one end and see a wave travel back and forth in the line. If that line is lighter, the wave travels faster. If the tension is higher, I THINK that the wave travels faster. THIS WOULD BE A GOOD EXPERIMENT.

For our purposes, electromagnetic energy, eg from the sun to the earth, travels in what are called photons. A photon is, in essence, a teeny tiny packet of energy, that has a wave-length. "In all such, the shorter the wavelength, the more energy it takes to create that photon, and the more energy the photon carries". You might repeat that. It's very important.

Heat, eg when you stand in sunlight, comes in longer wavelengths, and has less energy PER PHOTON than visible light. Ultravilot light, that can give you a sunburn, comes in shorter wavelengths, with more energy per photon. Radio waves, that transmit what you can hear on a radio, are MUCH longer -- ie lower energy PER PHOTON, than visible or ultraviolet or infrared, BUT, if you could see them, a radio tower puts out LOTS of them. If radio waves were visible light, they'd be blindingly bright all around us.

WHAT'S AN ATOM AND A MOLECULE, WHAT'S MASS AND WEIGHT

An atom consists of a nucleus, that contains protons and neutrons, and electrons that are around the nucleus. The number of protons = number of electrons. The + and - charges balance. The number of neutrons just add mass (weight).

Standing here on earth, we think of weight and mass as being the same. But if you're in the International Space Station, your weight is 0 but your mass is still the same. It can be thought of as, gravity gives mass weight. If you weigh 140 lbs here, on the moon you'd weigh 20 lbs, because gravity is lower on the moon. If you drive a nail into a board with a hammer, it takes the same force with the hammer, regardless of whether you're on earth, on the moon, or in the space station. The hammer has the same mass in all cases.

Compared to the size of the nucleus, the electrons are very far away. IF you were to compress the electrons into the nucleus, and have a teaspoon full of that stuff, it would way several tons. Lots of tons. You could drop it on hard rock and it would push its way through and head to the center of the earth.

https://sciencenotes.org/wp-content/uploads/2021/08/Parts-of-an-Atom.png

http://www.chem4kids.com/files/elements/art/019_orbital.gif

http://www.chem4kids.com/files/elements/019_shells.html

PERIODIC TABLE (is as basic to chemistry as numbers are to math)

https://ptable.com/ (if you're a geek, and I hope you are, this is cool)

There are 92 naturally occurring elements on earth, and everywhere else in the universe, no more, no less. (See More to think about at the end.) These elements can be combined in billions of different ways. When you take 2 or more, different elements, and combine them, the resulting compound is different, and very rarely at all like either of the original elements. EG. you can combine oxygen and hydrogen gases, and create water. Not at all like the original elements. In general, the science of combining elements is called chemistry. Interestingly, there is a really, really large subsection of chemistry, called organic chemistry, that really is the chemistry of living things. To some degree, it's the chemistry of carbon, because carbon combines with other elements in so many differet ways. Inorganic chemistry is everything else, including CO2.

Gases, other than 'noble gases' ( hydrogen, neon, argon, krypton, xenon, and radon ) will always combine with themselves. So, our air consists of nitrogen N2, and oxygen O2, and CO2, and water H2O, and more trace gases. If you look at ptable.com, one of the things it tells you is the number of electrons in the outer shell. To some degree, the number of electrons in the outer shell determines the chemical properties. When the periodic table was first invented, they didn't know about many of the elements, but what they did know was that some behaved like others, but were heavier, so when they created the periodic table, they left spaces for elements that they though existed.

DISTANCES AND SPEEDS

Our life experience doesn't provide us with a good way to compare very large, or small, distances, or speeds.

Out in space, the distance between stars is usually given in light years. A light year is a unit of distance, not a unit of time. A light year is the distance light travels in a year. That is 5,880,000,000,000 (or 5.88 trillion or 5.88*10^12) miles. Light travels from the moon to the earth in about 1-1/3 seconds. Light travels from the sun to the earth in 8 minutes. Light takes 82 minutes, from the sun to Saturn, and 5-1/2 hours, from the sun to Pluto. Light from the nearest star, Alpha Centauri takes 4-1/2 years to get to us. IF Alpha Centauri were to disappear (no, it can't do that) it would be 4-1/2 years before we knew that happened.

You might not remember the Space Shuttle, but it was a major part of the space program. It carried the Hubble Space Telescope up into space, and carried folks to it for 5 repair missions. There were a total of 135 Space Shuttle missions, 2 of which crashed. The Space Shuttle went about 18,000 mph. If it went straight to the moon, it would take about 16 hours to get there. The sun is much farther away. It would take 6 months to get to the sun. Think that's a lot?? The nearest star, Alpha Centauri, is 4-1/2 light years away, so it would take 170,000 years for the Space Shuttle to get there.

WHAT IS AN IDEAL GAS, and WHAT IS A MOL, and WHAT IS STP

First, stuff to know. What is STP? "Standard temperature and pressure (STP) refers to the 'nominal' conditions in the atmosphere at sea level. In science, you often need a common baseline to compare different things, so these conditions are 0 degrees Celsius (32° fahrenheit or freezing) and 1 atmosphere (atm) of pressure."

When reading math equations, you know what + and - are. * means multiply. / means divide. ^ means exponent. For example 3+2=5 3*2=6 3^2 = 3 squared or 3 to the 2nd power, 3^2=3*3=9.

What is a mol? 6.02*10^23 atoms or molecules, regardless of the specific substance in question. What's the volume of a mol? At STP, one mole (6.02×10^23 representative particles) of any gas occupies a volume of 22.4L (liters) or about 6 gallons or 0.8 (4/5) cubic feet. (No, I don't know why they chose that volume.)

Gases are very interesting. If you have a bottle of hydrogen, or helium, and a bottle of CO2, the CO2 bottle is heavier because CO2 is heavier. However, if you count the number of molecules in the 2 bottles, they will be the same.

https://en.wikipedia.org/wiki/Ideal_gas_law

There's an equation, involving the pressure, temperature, volume, and number of molecules.

p*V=n*R*T Pressure * Volume = number of molecules (or atoms) * Temperature * ideal gas constant, at STP.

Note that, the weight of the gas is nowhere in that equation, only the number of molecules.

You know that gases expand as they get warmer, and also expand as you go higher, and the pressure decreases, that's why, in physics, STP is important -- you want a consistent baseline.

H2O AND CO2 (We're getting there, we really are)

https://www.researchgate.net/figure/Sketch-of-vibrational-modes-of-CO2-left-and-H2O-right-The-vibrational-frequencies_fig4_287258623

This shows the vibration modes of CO2. For global warming, we're only interested in the bottom one, because that's the lowest energy (ie lowest frequency) vibration mode, and also energy mode. Water really only has a vibration mode like the 3rd one. Our atmosphere generally consists of 78% nitrogen, 21% oxygen, and 1% water, CO2, and trace gases.

If you've seen a tuning fork, you know it has a specific frequency -- plays a specific note. There's an experiment in which sound, of the correct frequency, can break a wine glass. That happens when the frequency of the sound matches the natural frequency (ie frequency at which the glass likes to vibrate) of the glass. As the sound gets louder, the glass vibrates more, until it shatters. That's 'resonant frequency'. Most gases also have a natural frequency -- in the case of CO2, more than one, depending on the mode of vibration. The molecular H2O and CO2 are in the neighborhood of the frequency of infrared radiation. What that means is that, radio waves, and visible light waves, and ultraviolet waves do not affect either CO2 or H2O. But, when there's infrared wavelengths, then CO2 and H2O do absorb photons. And then they emit photons, gaining and losing energy, maintaining a balance. However, just like on a cloudy day, sun light seems to come from everywhere, the photons emitted by CO2 and H2O are emitted in random directions -- some toward outer space, some down to the ground, and in every direction. When you turn on a light bulb, the light goes in every direction. It's the same. In a situation like this, photons get absorbed and emitted repeatedly.

https://andthentheresphysics.wordpress.com/2017/10/21/infrared-absorption-of-atmospheric-carbon-dioxide/

THE SUN

In the sun, energy is created, at very high energy levels, and is absorbed and emitted within the sun, often traveling small fractions of an inch. It takes 1,000,000 years, on average, for energy created in the middle of the sun to reach the surface. (And then 8 minutes to get to earth, because there's no matter in between to interrupt it.)

TEMPERATURE OF THE EARTH

The temperature of the earth is controlled by how much energy it receives from the sun, heating it, and how much energy it loses (sheds) by radiating infrared radiation away. The average temperature is maintained when those two balance each other. If there is an imbalance, then the world either get warmer or colder, until there is a balance again.

GLOBAL WARMING (I told you we'd get here)

What's happening today is that there is about 50% more CO2 in the atmosphere, so more infrared energy is intercepted, and retained, causing warming.

TODAY'S EXPERIMENT

We're going to do several experiments, with two, 2 liter bottles of air, and with CO2, with a thermometer in each bottle, and with an LED light, and a heat lamp. To set it up, carefully measure the distance from the lamp to 2 locations, in a direct line, so you can shine a light through both bottles in a row. You're going to shine one light, or the other, for 1 minute, through one or both bottles, and record the lamp used, temperature at the end of 1 minute, and whether the bottle, or bottles, contain air or CO2. When setting up, put the first bottle a foot away from the light source, and the second bottle as close as possible, without touching.

- Shine the LED bulb, first through the air bottle, then through the CO2 bottle for 1 minute each, and record temperatures.

- Similarly, shine the heat lame (infra red light) through each bottle, and record the temperature.

- Line the bottles up so that light shines directly through both of them, with the air bottle first, then the CO2 bottle, and record temperatures.

- Reverse the bottles, so the CO2 bottle is first, then the air bottle, shine the light, and record the temperatures.

- If you have two CO2 bottles, line them up, and shine the light through both of them and record the temperatures.

- You could next line up the air bottle and then the 2 CO2 bottles, and again record temperatures.

RESULTS

What you should see is that the CO2 bottle's temperature rises, and the air bottle's temperature does not. The plastic might obscure that a bit, but you should see the difference.

If you have 2 CO2 bottles, and put one in the 2nd location, and measure the heat rise, and then put a second CO2 bottle in front it the first one, the first bottle should extract some of the energy, and the temperature in the second bottle should not rise as much.

Air bottles shouldn't do much of anything, other than show whether the bottle itself, warms. The air inside the bottle is the same as the air without the bottle, so putting the air bottle in the energy stream only tests the plastic.

MORE TO THINK ABOUT (ozone)

Ozone is O3, as opposed to O2, which is what we breathe. Ozone is formed very high in the atmosphere, fortunately for us. It has a resonant frequency, like H2O and CO2, but much higher. What that does is allow it to interact with ultraviolet light, and scatter it out to space, rather than coming directly down to earth. That's good because even what little of it does make it down, causes sunburn. Life would be more dangerous without it. Some years ago, there was a big to-do, because there was a hole in the ozone layer, down in the antarctic. Ozone was being destroyed by chemicals that we were releasing into the atmosphere, that we didn't know caused a problem. Once the problem was understood, people stopped making those chemicals, and the ozone hole is getting smaller. Not done yet, but it's getting better. This is, however, another example of how molecules intercept specific wavelengths / energy levels, and not others.

92 Elements. Atomic fusion is what powers stars. Sometimes we talk about "burning hydrogen", but that's not correct. Burning implies using oxygen. Fusion does not do that. But both processes, burning and fusion, use up "hydrogen in this case" so in that respect they're vaguely similar. Stars fuse hydrogen into helium, and then into lithium, etc. Large stars fuse more elements up to iron. Small stars, like our sun, don't have enough gravity to create iron. Fusion stops when iron is created. That process generates so much heat energy that the star blows up. That process creates the heavier elements, and then some percentage of everything is blown out into space. That happened before our sun, and the solar system, were created. That's why we have copper, zinc, chromium, lead, mercury, uranium, etc. I expect that elements heavier than uranium are created, but they are unstable, and break down, so there are none left - at least none that we can find.