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FIRE!
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DR. IFFIC: FIRE!
Hello and welcome to our second lecture. Last :me, we reviewed the four fundamental forces of the universe and sorted out the roman:c life of
protons and electrons. Dmitri Alekseyevich, what ques:ons have arrived from the clamoring masses of adulatory knowledge seekers?
We have a ques:on from an individual purpor:ng to be named “Jimmy,” who asks,
“Dr. Iffic, what exactly is fire?”
NOT “JIMMY” AT ALL.
“Jimmy,” eh? A likely story. Very well, “Jimmy.” The nature of fire is not quite as tripped-‐out crazy as you may imagine, but in order to understand fire, you
must first understand heat. And heat, in a word, is jiggling.
Jiggling?
JIGGLING, Dmitri Alekseyevich. Pure and simple.
Do you mean to say that if I jiggle this nonbranded toaster pastry, it will become warm and delicious?
Well, it is already delicious. But the heat of the nonbranded toaster pastry is not determined by the jiggling of the en:re pastry. It is determined by the jiggling of each and every
individual molecule within the pastry. That is what heat energy is – the jiggling of molecules.
And molecules are :ny li\le bits of something, is that right?
More or less. Molecules are collec:ons of atoms that are stuck together very :ghtly because of what their electrons are doing. And molecules are always jiggling back and forth
to some degree. The jiggling is so small that we can’t see it. But we can sense it, and observe it, as heat. Hot molecules are jiggling fast. Cold molecules are jiggling slower.
MOLECULE
atom
atom
atom atom
atom
Cold = slow Hot = fast
It is jiggling already, Dmitri Alekseyevich. It is at room temperature, which requires a certain amount of jiggling. If you put it in the freezer, it would jiggle slower, but there would s:ll be some jiggling going on. In theory, if your pastry stopped jiggling altogether, it would be at
absolute zero temperature – but it’s impossible to stop all the jiggling in a molecule.
Incredible jiggling
Intense jiggling
Moderate jiggling
Very li\le jiggling
Absolutely no jiggling
It’s strange to think that my pastry will jiggle once I toast it.
The cells in your body can’t operate correctly when they’re jiggling too fast. And when cells can’t operate correctly, they die. So when your nerves sense that the jiggling is
geang to dangerous levels, they send a message to your brain saying, HOOLABALOOLA! GET YOUR HAND OFF THAT HOT THING, YOU CELL-‐KILLING IMBECILE! The fact that heat is jiggling doesn’t mean it’s no big deal – too much jiggling, or not enough jiggling, is
very dangerous for living things.
If heat is just jiggling, why does it hurt to touch something hot?
For example, fire, indeed. Fire will jiggle you to a crisp before you can say, HOOLABALOOLA! And what use will your nonbranded toaster pastry be to you then?
For example, fire.
Fire is actually gas that is jiggling so fast that it glows.
Jiggling can make something glow?
So what IS fire?
Yes indeed. You see, the jiggling energy that is heat does not stay in one place. It has a tendency to spread out as much as possible. One way it
spreads out is when molecules touch each other. The faster-‐jiggling, ho\er molecules transfer some of their jiggling energy to the slower-‐jiggling,
colder molecules, un:l everything is jiggling the same amount.
That makes sense.
Also, molecules can reduce their jiggling energy by shoo:ng out a photon, or absorb a photon and transform it into jiggling energy.
Well, essen:ally it is, although it acts like a wave too, which is one of the more tripped-‐out crazy aspects of science.
So super-‐hot things start shoo:ng out photons?
OK, that’s a li\le weird. Isn’t a photon just a :ny li\le par:cle of light?
Not just super-‐hot things, Dmitri Alekseyevich. You and your nonbranded toaster pastry are shoo:ng out photons right now, and absorbing photons that got shot out from other things.
But I’m not glowing! Nor is my nonbranded toaster pastry!
Remember, Dmitri Alekseyevich, not all photons are visible to our eyes. Radio waves, microwaves, and gamma rays are all made of photons, but we can’t see
them, even though we can use them to transmit informa:on, cook frozen burritos, and turn people into the Hulk. Because photons behave like waves, they have frequencies, and different frequencies create different forms of radia:on.
Radio Waves Microwaves Gamma Rays
Think of the strings on a guitar. If you play them at one set of frequencies, you get Mary Had a Li\le Lamb.
Similarly, while photons at one frequency produce a beam of yellow light, at a different frequency they produce microwaves.
whereas if you play them at another set of frequencies, you get the latest hit by the Icelandic death metal band Sküllmelter.
They are at the infrared frequency, which is the frequency of most heat-‐related photons, and which is invisible to us, unless we are commandos with super cool
thermal imaging goggles.
OK, so why can we see fire?
So what frequency are the heat-‐related photons coming out of me and my nonbranded toaster pastry?
Fire is made of gas that is so superhot that it is also spiang out photons that we can see. When burnable stuff gets hot enough, its molecules jiggle so fast that they fly apart into plain old atoms. For example, wood is made of organic molecules that include carbon, oxygen, and
hydrogen. Here’s a diagram that shows where the atoms are and how they are bonded together.
C
C O
H
H H
H C
C
H
lots more stuff
lots more stuff
When these molecules fly apart, the carbon atoms interact with the oxygen molecules in the air to form carbon dioxide.
C O
O
C
C
O
H
H H
H
C O
O
And when carbon atoms join with oxygen molecules to make carbon dioxide, it creates a tremendous extra kick of jiggling heat energy. So the superhot carbon dioxide molecules shoot
out all kinds of photons, including red, yellow, or blue ones that we can see.
They also float upwards, because hot gases tend to float on top of cool gases. But as they float, they cool down. Pre\y soon they cool down enough so that they are no longer shoo:ng out
visible photons, just the invisible infrared ones that everything shoots out.
C O
O C
O
O
C O
O
C O
O
C O
O
It’s not really jumping. The superhot glowing gas is so hot that if another chunk of burnable stuff gets too close, its own carbon molecules will heat up, fly apart, and
start making their own superhot glowing gas.
So how can fire jump from one burning thing to another if it’s just gas?
Including my nonbranded toaster pastry.
Correct.
C
C O
H
H H
H C
C
H
lots more stuff
lots more stuff
C O
O
C O
O
C
C
O
H
H H
H
C O
O
C O
O
Correct in every respect. Now let us bombard your nonbranded toaster pastry with photons
un:l it jiggles at a more delicious rate.
So, to recap: fire is superhot glowing gas, heat is jiggling, and my nonbranded toaster pastry
and I are constantly shoo:ng out and absorbing invisible photons.