Why is fire hot? An answer to the question commonly asked by children.

Two years ago I renovated an old farmhouse in France. One the first things we had fitted was a beautiful, cast iron wood burner in the lounge. Upon lighting the fire, I told my little boys to keep their distance for obvious reasons. My eldest son asked “Dad, why is fire hot?”, a question I didn’t know the answer to. So I decided to do my research…

Fire is a chemical process involving the rearrangement of molecules. You may or may not remember from your schooldays that molecules comprise several atoms bonded together. Whenever molecules rearrange their atoms during such a chemical change, energy is either released or absorbed. With fire, the release of energy takes the form of heat (and light), which is basically why fire is hot. But let’s look at things in a little more detail…

Three things are needed to trigger the aforementioned chemical process and start a fire – oxygen, fuel and heat/an ignition source (e.g. a match, focused sunlight, etc). The chemical process is called oxidation. To give a familiar example of oxidation, when iron rusts, oxygen in the air combines and reacts with iron atoms (without having the scope to go into too much detail, electrons basically pass from the iron to the oxygen). This chemical reaction between the oxygen and iron releases energy. In the case of corroding iron, the oxidation rate and release of energy is extremely slow and so the rusting area increases only very slightly in temperature. But in the case of fire, the oxidation rate (which in the case of a wood fire for example occurs between oxygen, hydrogen and carbon atoms) and resulting release of energy is very fast and thus a lot more heat is produced.
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Of course, a pile of wood won’t just catch fire because it is surrounded by oxygen! For the combustion (i.e. burning) to take place you need the third element mentioned above – heat – to make the fuel reach its ‘ignition temperature’. If heat cannot be released faster than it is created then combustion happens. So, for example, sliding a match fast enough across a coarse surface will generate sufficient heat (due to friction) to produce a temperature which is at least as high as the chemicals within the match head’s relatively low ignition temperature, and it will ignite. The resulting combustion provides even more heat and the match will often continue to burn until the fuel (stick) runs out.

So, once something is ignited, enough heat needs to be maintained/produced to keep the fuel and oxygen at or above its ignition temperature and keep the fire going. It is a chain reaction of sorts in that the fire must sustain its own heat and have an ongoing supply of oxygen and fuel to keep going.

Phew, that’s a lot to try to take in! But in summary, fire is a chemical process called oxidation and requires oxygen, fuel and a heat source. During this process, the chemical bonds in oxygen and fuel are rapidly broken and new bonds are formed. Although some energy is used up when chemical bonds are broken, more is released during the creation of the new ones. That extra energy is released as heat, which is why fire is hot.

Read more: http://scienceray.com/technology/why-is-fire-hot/#ixzz1JD8qDEnz

Woody

Like Ian Fleming and P.G. Wodehouse, Woody Allen returns compulsively to the same creative ground. In Allen's case, it's ground trod by anxious, well-to-do white people, who swap partners and drop cultural references in an empty, godless universe. The extent of the similarities from one film to the next is remarkable. It's not just that he recasts actors or that he revisits the themes of domestic boredom and cosmic insignificance. He reuses the same font, EF Windsor Light Condensed, for his titles and credits. He recycles character types: the neurotic Jewish New Yorker (the filmmaker's spit and image), the adulterous intellectual, the hypochondriac intellectual. He recycles plot lines. He even recycles punch lines. In Celebrity (1998), a model says she's "polymorphously perverse … meaning every part of my body gives me sexual pleasure." That should sound familiar: In Annie Hall (1977), Alvy tells Annie that she's "polymorphously perverse … you get pleasure in every part of your body when I touch it."
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Given the redundancy of Allen's work, it might seem like a waste of time to dig into it deeply and get beyond his top-tier comedies and dramas. Yet attending "the new Woody Allen" is, for me, an annual rite. The worrisomely prolific auteur has written and directed 40 feature-length films, and has a 41st scheduled to premiere at Cannes in May. I have seen them all, as well as the early movies that he wrote but did not direct (What's New Pussycat?, Play It Again, Sam), the shorts Oedipus Wrecks and Sounds from a Town I Love, and the TV movie Don't Drink the Water. I've even watched Men of Crisis: The Harvey Wallinger Story, a 25-minute mockumentary that satirizes the Nixon administration. Produced as a television special for PBS, it was pulled before airing, reportedly because the programmers feared antagonizing government officials. (I tracked it down at the Paley Center for Media.) Lots of cinephiles can quote the best lines from Love and Death. Sonja: "Sex without love is an empty experience." Boris: "Yes, but as empty experiences go, it's one of the best!" I can cite jokes from Take the Money and Run: "I think crime pays. The hours are good, you meet a lot of interesting people, you travel a lot." Or from Stardust Memories: "To you I'm an atheist; to God, I'm the loyal opposition."

One might detect in my behavior a trace of the repetition compulsion that animates Allen. In my defense, and in his, consider this: Though he returns to the same themes, I've found significant differences in how he treats those themes—variations not attributable to basic shifts in genre (comedy versus drama) or to fluctuations in quality. (Sadly, I must admit he is far from consistent in this regard. Celebrity and Hollywood Ending belong in a bonfire.) There's also diversity in the way Allen's characters grapple with the ideas that preoccupy him, particularly in the way they handle the likelihood that we live in a godless universe. Allen answers the question of what we should make of nothingness differently in different movies. Sometimes nothing means everything, sometimes nothing much.

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When an Allen character is in a particularly morose state of mind, he may feel moved to announce that life is meaningless. I call these "void moments," because the declarations often contain the word void. Despite the bleak moniker, the void moment doesn't always have the same function. Play It Again, Sam (1972), for instance, has a particularly lighthearted one.

In this little-seen comedy, the recently divorced Allan Felix (Woody Allen) tries to get the hang of dating. Trouble is, he's romantically self-destructive: Felix (I'll use his surname to avoid confusion) says he's attracted to "emotionally disturbed women," and that's not an exaggeration. The depth of his perverse inclination becomes clear when he approaches a woman looking at a Jackson Pollock drip-painting, and asks what it means to her. She answers: "It restates the negativeness of the universe. The hideous, lonely, emptiness of existence. Nothingness. The predicament of man forced to live in a barren, godless eternity like a tiny flame flickering in an immense void with nothing but waste, horror, and degradation forming a useless bleak straightjacket in a black absurd cosmos." She's just the kind of woman Felix has been looking for, and he asks her what's she's doing Saturday night. "Committing suicide," she responds. Unfazed, he counters: "What about Friday night?"

This nameless woman seems to articulate Allen's world view exactly. (After the 2009 release of Whatever Works, he told NPR that filmmaking "distracts me from the uncertainty of life, the inevitability of aging and death and death of loved ones; mass killings and starvation, from holocausts—not just man-made carnage, but the existential position you're in." Inspiring!) But in Play It Again, Sam, we're clearly meant to find her approach ridiculous. The depressive despairs: Because there is "nothing," she longs to return to that state. Felix, by contrast, moves forward blithely: If existence is lonely and hideous, why not go out on Saturday? Or Friday, whatever, he's not busy. By letting Felix win the volley, Allen also endorses his protagonist's resigned epicurean sensibility.