Thermal equilibrium
A spoon in hot soup
- Put a cold spoon in hot soup: the spoon warms, the soup cools — until they match.
- Energy moved from the hot thing to the cold thing.
- That one-way flow is the key idea of temperature.
Heat flows hot to cold
- Heat (thermal energy) flows from higher to lower temperature.
- It keeps flowing until the temperatures are equal.
Practice
Heat (thermal energy) naturally flows from:
Energy always flows down the temperature difference, from hot to cold, until they are equal.
Thermal equilibrium
- When two things reach the same temperature, they are in thermal equilibrium.
- There is then no net flow of energy between them.
Practice
At thermal equilibrium there is no net flow of energy between two bodies.
Equal temperatures mean no net flow — particles still exchange energy, but with no overall transfer.
Practice
Two objects in thermal equilibrium are at the same ____.
Same temperature is exactly the condition for thermal equilibrium.
Temperature is not energy
- Temperature decides the direction of heat flow — not how much energy a body holds.
- A tiny spark at $1000\ °\text{C}$ holds far less energy than a warm swimming pool.
Practice
Temperature tells you:
Temperature decides the direction of heat flow; the amount of energy also depends on mass and material.
Practice
A hot spark always contains more thermal energy than a warm swimming pool.
No — the spark is at a higher temperature, but the huge pool holds far more thermal energy overall.
You've got it
Key idea
- heat flows from higher to lower temperature
- thermal equilibrium: equal temperature, no net energy flow
- temperature sets the direction of flow, not the amount of energy