Heat and temperature
Heat and temperature are not the same. Temperature measures how fast particles shake; heat is energy moving from the hot body to the cold one, always in that direction. What almost nobody expects is what happens at a change of state: while ice melts the temperature does not rise, even with heat still going in, because all that energy goes into pulling particles apart rather than shaking them faster. A glass with ice stays at zero until the last piece melts.
Where this sits
- Comes after
- Energy
Exercises from this rung
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While the ice melts, what does the temperature do?
- It stays the same
- It falls
- It rises slowly
- It rises fast
Why It stays stuck at 0 °C. That is what almost nobody expects: heat is going in and the thermometer does not move. The energy is not lost, it is spent breaking the ice's structure; as soon as the last piece melts, the temperature starts rising again.
easierYou mix a litre of water at 78 °C with another at 22 °C. What temperature do you get?
Answer 50
Why At 50 °C, the average of the two, because there is the same amount of each: heat flows from the hot body to the cold one until both are equal, and never the other way. With different amounts, the result would lean towards the bigger one. (lead melts at 327 °C, to get a sense of scale.)
in betweenYou touch metal and wood in the same room. Which feels colder?
- Both the same
- The wood
- It depends on the colour
- The metal
Why The metal, and yet both are at the same temperature: what you feel is not the object's cold but how fast it takes heat from your hand. Metal conducts fast and wood does not, so the same temperature feels very different. “Cold” is a sensation of flow, not a measurement.
harder