eli5. How do table saws with an auto stop tell the difference between wood and a finger?
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Electricity.
The saws that can detect that stuff have a tiny current constantly flowing through the running sawblade. Wood, being wood, does not conduct electricity very well, and so there’s not much change in that current when wood contacts the saw. Thumbs, being sweaty and made of meat, conduct electricity a bit better than wood, and so they change the current in the sawblade more.
When the saw detects a change in the current, it fires a mechanism that punches an aluminum block into the saw, stopping it immediately.
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