Two objects, one temperature: how heat reaches agreement

Lesson author: Яна Костова · EASYPhysics

Why must a thermometer settle, and why can metal and cloth fool your hand? Explore equilibrium and predict the final temperature.

Your mission is to predict what happens when a warm object touches a cooler one. In Pavlo Viktor’s lesson on temperature, the hot block cools while the cold block warms. When their temperatures match, there is no net energy transfer between them driven by a temperature difference. This is thermal equilibrium.

Predict first. Two identical blocks of the same substance start at 80 °C and 20 °C. In an isolated system their final temperature is 50 °C. The warm block loses as much energy as the cooler block gains. Neither side “wins”: energy balances.

Test it in the model. Set those temperatures and move progress to 100%. Then double the mass of A. The equilibrium temperature becomes 60 °C because the larger block has a greater heat capacity. For the same substance, with no losses or phase change, t = (m₁t₁ + m₂t₂) / (m₁ + m₂). The simple average works only for equal masses. Different substances also require their specific heat capacities.

Your hand is not a thermometer. The classroom example compares a glass cube and a fabric toy that have been in one room for a long time. They feel different because they exchange energy with your hand at different rates. “Feels colder” does not necessarily mean “has a lower temperature”.

Why wait for a reading? A thermometer initially has its own temperature. It exchanges energy with the object and approaches equilibrium. Settling time depends on the instrument and its instructions; there is no universal ten-minute rule.

Final challenge: both blocks start at 30 °C. Would doubling one mass cause heat to flow between them? No temperature difference means no net heat transfer between the blocks. Try it, then open the Thermometer mission in the games section.

This is our educational interpretation for clear understanding and visual exploration, not a verbatim transcript. Original video: Pavlo Viktor, Thermal equilibrium and temperature. Thank you for teaching learners to reason.