Al Stahler: Energy – give and take |

Al Stahler: Energy – give and take

Energy from the sun pulls water up from the tropics – pulls water both up into the air, and up towards the north. Over the foothills, some of that water comes down as rain.

Given its druthers, that rainwater would flow downslope, back to the sea. But dams get in the way, keep that water high on the slopes. We do, eventually, allow that water to flow downslope, but along the way, we make it spin wheels, to generate electricity. By allowing the water to do what it wants, we reclaim some of the energy the water absorbed from sunlight.

Green plants harness the energy of sunlight to pull atoms out of air and water. They then use the sun’s energy to push the atoms together, making them STICK together. The atoms don’t want to stick together – they’d rather be back in the air – but the plant forces them together, into molecules – structures built of atoms.

Faced with an unfamiliar word, we try to figure it out by looking for clues. Words ending in “-ing,” for instance, are action words: running, jumping, reading.

Chemists put all sorts of such clues into new words. If a word ends in “-ose,” it’s a sugar: lactose is milk sugar; fructose, fruit sugar. The sugar sold in supermarkets is sucrose.

Green plants harness sunlight to assemble atoms into molecules of glucose. This takes energy, because the atoms would rather remain in the air … but the energy does not disappear. It is, rather, stored in the molecule of glucose. The plant can later reclaim that energy, by allowing the atoms in glucose to return to the air … much as we reclaim energy by allowing water to flow back to the ocean. Animals (like ourselves) eat plants to get at the energy they’ve stored.

A tree takes things further. It glues molecules of glucose together to make yet-larger molecules of cellulose – a sugar we cannot digest (though the microbes in a termite’s gut can). Cellulose is a major component in wood.

The atoms in wood don’t want to be stuck together any more than the atoms in sugar do. If we allow the atoms in wood to get back to where they’d rather be – back to air and water – we can reclaim the energy the tree used to assemble the cellulose. We get that energy back by setting the wood on fire.

Over a century ago, a chemist figured out how to turn atoms from air and water into fertilizer. Heating the atoms to a thousand degrees Fahrenheit … and squeezing the atoms under two tons per square inch pressure … he could force the atoms to re-arrange themselves, and stick together.

We still, today, thus make ammonium nitrate fertilizer. Like the atoms in sugar or wood — like the water held upslope — the atoms in ammonium nitrate would rather be elsewhere … would rather be back in the air, in water

Treat it right, and ammonium nitrate can hang around more-or-less forever. But get it hot, and the atoms bounce around … cannot hold onto each other … and scramble back to where they’d rather be — fast. I got in touch with Alex Djerdjev, University of Sydney, who studies the safe use of ammonium nitrate.

Recall the conditions needed to make ammonium nitrate: a temperature of a thousand degrees, two tons per square inch pressure. When the atoms are allowed to go back to the air, to water, they release a LOT of energy. Ammonium nitrate finds use, today, in the gold mines of California. It’s also still used, today, as fertilizer … but is just as explosive, as was revealed, tragically, in Beirut.

A thousand years ago, a new star appeared in the sky. It was bright – bright enough, according to Chinese astronomers, to shine, for several weeks, in a blue, daytime sky.

Searching the stars of Taurus with binoculars, we find today, a fuzzball. With sophisticated telescopes, astronomers find the remnants of what the astronomers had seen – a star that died in an explosion so violent, it could be seen – during the day – on Earth, 40 million, billion miles away.

Conditions inside that exploding star were super-hot, super-squished. Hot enough, squished enough, to force subatomic particles – protons and neutrons – to stick together, to create atomic nuclei that could not otherwise be forced to hold together … uranium nuclei, for instance.

The protons and neutrons in the uranium nucleus would rather be elsewhere … so much so that, unprompted, they dribble, slowly, out of the nucleus. Constantly emitting subatomic particles, uranium is radioactive.

In the late 1930s – with the world about to plunge into war – physicists discovered how they could goose uranium nuclei, to make the particles unstick. As with falling water, as with burning wood, we reclaim energy – in this case, the energy of exploding stars – when we allow sub-atomic particles to do what they want. Goosing the uranium nucleus to split released a HELL of a lot of energy, seventy-five years ago, over Hiroshima and Nagasaki.

Before the bombing, over a hundred physicists signed a petition to the president, asking that the bomb not be dropped on a city … but the decision was out of their hands.

Saturday morning, before dawn, the crescent moon will sidle up close to the morning “star” — planet Venus. In the southern sky, planet Mars will shine.

All the light we get from Venus (and from Jupiter, high and bright in the south after sunset) is sunlight reflecting off cloudtops. But looking at Mars – high in the southern sky, before dawn – we’re seeing its surface. Light coming from Mars is sunlight reflected off the dust of the Martian desert … and that dust is a deep, rusty red.

Al Stahler enjoys sharing science and nature with friends and neighbors on KVMR-FM, teaches science for kids and grown-ups, and can be reached at

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