Perfect scissors

About this video

Take a strip of kitchen foil and cut it in half. Then cut one half in half, and again, and again. Most people manage seven or eight cuts before the piece is too small to hold. But imagine perfect scissors and perfect eyes. Could you go on cutting for ever, or would you reach a piece that cannot be cut any more? With perfect scissors you would need only about twenty more cuts to reach a single atom of aluminium: the smallest piece that is still aluminium.

People asked this question long before anyone could check it. About 400 BCE, in ancient Greece, Democritus said you could not cut for ever: in the end you would reach tiny pieces that cannot be cut. He called them atomos, Greek for uncuttable. For more than two thousand years nobody could prove him right or wrong. Then in 1808 an English teacher, John Dalton, showed that the way substances combine makes sense only if they are made of tiny pieces, each with its own weight. Today we call them atoms.

Atoms are far too small to see, even with the best magnifying glass. A human hair is about a million atoms wide, and a single grain of salt holds more atoms than there are grains of sand on a beach. Everything is made of them: the air, the water you drink, your chair and your own body. A tiny particle of water is a group of three atoms, one oxygen and two hydrogen. This video goes with the lesson Cut It in Half Again in Chemistry Level 1 on Knaph.

Transcript

1. 0:00Cut a strip of foil in half. Again. And again. After seven or eight cuts, your scissors stop.
2. 0:11With perfect scissors, about twenty more cuts would leave one atom of aluminium.
3. 0:20About 400 BCE, Democritus called these pieces atomos, uncuttable. In 1808, John Dalton showed they were real.
4. 0:28Atoms are tiny. A human hair is about a million atoms wide.
5. 0:35A tiny particle of water is three atoms. Everything is atoms.
6. 0:41Keep cutting, and in the end you reach an atom.