Thermal energy flows from hot to cold, and stops when temperatures match. That balance point is thermal equilibrium, and it is what a thermometer relies on.
Thermal energy flows from regions of higher temperature to regions of lower temperature. Two bodies at the same temperature are in thermal equilibrium, with no net flow between them.
Bring a hot object and a cold one together and energy crosses the boundary from hot to cold. The flow slows as the gap narrows and stops when the temperatures are equal. Set two starting temperatures in the simulation and watch them meet at the average.
Two bodies are in thermal equilibrium when there is no net transfer of energy between them, which happens precisely when they are at the same temperature. Temperature tells you the direction of any net flow, not how much energy a body stores: a cool swimming pool holds far more internal energy than a hot cup of tea, simply because it contains so many more particles.
Four quick checks on the direction of energy flow and the meaning of thermal equilibrium. Each correct answer earns XP and lights this skill on your star map.
When two objects at different temperatures are placed in contact, the net flow of thermal energy is:
Two bodies are in thermal equilibrium when:
A cup of tea and a swimming pool are at the same temperature. Compared with the tea, the pool has:
The temperature of an object determines:
Temperature is not the same as thermal energy. A large cold object can hold more internal energy than a small hot one; what flows between them is energy, and its direction is set only by the temperature difference. Equal temperature means no net flow, even if the two bodies store very different amounts of energy.
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