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How do you time a flash of light with two clocks?

Timing light from one place to another seems to need only a clock at each end. But the clocks must first agree on what time it is. Einstein's synchronization procedure makes that requirement explicit by sending a signal out and back and relating the two journeys.

5–7 min

Questions you could explore

  • What changes when the entire round trip can be timed with one clock?

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Physics

Why metal can feel colder than wood

A metal handle and a wooden tabletop can share a room temperature yet feel quite different. The clue lies in the exchange of heat between your hand and the surface, which is not the same thing as measuring temperature.

5–7 min

Why metal can feel colder than wood

Physics5–7 minA metal handle and a wooden tabletop can share a room temperature yet feel quite different. The clue lies in the exchange of heat between your hand and the surface, which is not the same thing as measuring temperature.

Physics

How can headphones fight noise with more sound?

A steady engine hum can fade when noise cancellation switches on, while a nearby voice remains noticeable. The electronics and the physical ear covering do different jobs, and neither makes every sound disappear.

4–5 min

How can headphones fight noise with more sound?

Physics4–5 minA steady engine hum can fade when noise cancellation switches on, while a nearby voice remains noticeable. The electronics and the physical ear covering do different jobs, and neither makes every sound disappear.

Physics

How can a ship made of steel float?

A solid piece of steel sinks, yet a steel ship can carry people and cargo. Its hollow shape changes how much water the whole vessel can push aside, making the material alone an incomplete explanation of floating.

3–5 min

How can a ship made of steel float?

Physics3–5 minA solid piece of steel sinks, yet a steel ship can carry people and cargo. Its hollow shape changes how much water the whole vessel can push aside, making the material alone an incomplete explanation of floating.

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