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If A is in thermal equilibrium with B and with C, what does the zeroth law say about B and C?

If A matches B and C, then B matches C.

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  1. B and C have different temperatures
  2. B and C share a temperature ✔
  3. Nothing until B and C touch

Why: If system A is separately in thermal equilibrium with B and C, then B and C are in equilibrium with each other. This transitive relation makes thermometers meaningful.

Huh, didn't know that: Thermal equilibrium means no net heat transfer after systems are placed in thermal contact.

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The zeroth law introduced everyone because their temperatures matched.
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References

Answer: B and C share a temperature. If system A is separately in thermal equilibrium with B and C, then B and C are in equilibrium with each other. This transitive relation makes thermometers meaningful.

  1. OpenStax University Physics Volume 2, Thermodynamic Systems openstax.org/books/university-physics-volume-2/pages/3-1-thermodynamic-systems
    If object 1 is in thermal equilibrium with objects 2 and 3, respectively, then objects 2 and 3 must also be in thermal equilibrium.
    Checked 2026-10-10.

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