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How did a strip of foil capture a voice?

An early tinfoil phonograph turned a voice into a physical trace. Sound vibrated a needle as a foil-covered cylinder moved, leaving marks another needle could follow to replay the sound. The recording surface was fragile, making this a striking but limited way to preserve a moment.

3–5 min

Questions you could explore

  • What has to move during recording and playback?
  • How is a groove different from a digital audio sample?

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Engineering and inventions

How GPS finds you, and fixes its clock

Your phone can work out where it is by listening to signals from far above Earth. But turning a signal's travel time into a distance also creates a clock problem: the receiver must account for its own timing error.

12–15 min

How GPS finds you, and fixes its clock

Engineering and inventions12–15 minYour phone can work out where it is by listening to signals from far above Earth. But turning a signal's travel time into a distance also creates a clock problem: the receiver must account for its own timing error.

Engineering and inventions

Across an ocean inside a fiber-optic cable

A message crossing an ocean can travel through glass fibers lying on the seabed. The light inside, the layers around it, and the equipment along the route each solve a different problem.

8–10 min

Across an ocean inside a fiber-optic cable

Engineering and inventions8–10 minA message crossing an ocean can travel through glass fibers lying on the seabed. The light inside, the layers around it, and the equipment along the route each solve a different problem.

Engineering and inventions

Why does one pedal turn take you different distances?

Changing bicycle gears changes the relationship between your pedals and the rear wheel. The teeth on the chainring and sprocket help explain why the same turn of the pedals can produce a different distance along the road.

3–5 min

Why does one pedal turn take you different distances?

Engineering and inventions3–5 minChanging bicycle gears changes the relationship between your pedals and the rear wheel. The teeth on the chainring and sprocket help explain why the same turn of the pedals can produce a different distance along the road.

How did a strip of foil capture a voice? | Speech Topic | speaking.app