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Hot things cool down

Heat and matter · level 1, lesson 5 of 6

A question to start

Leave a cup of hot chocolate on the table, and an ice lolly next to it. What happens to each of them?

The idea

Hot things cool down until they are as warm as the room around them. Cold things warm up until they are as warm as the room too. In the end, everything left in a room gets to the same temperature as the room.

hot chocolateice lollyroomtime

The bigger the difference from the room, the faster it changes. A very hot drink cools quickly at first, then more slowly.

Worked examples

1. Hot chocolate. At first it is too hot to drink. After a while it is just right. Leave it for an hour, and it is cold: the same as the room.

2. An ice lolly. It warms up and melts into a puddle, which ends up as warm as the room.

3. A bath. If nobody gets in, the warm water slowly cools to the temperature of the bathroom.

Try it

  1. What happens to a hot drink left on a table?
  2. What happens to an ice cube left on a plate?
  3. Will the drink ever get colder than the room?
  4. Why do we put a lid on a pan of soup to keep it hot?
Answers
  1. It cools down until it is as warm as the room.
  2. It warms up, melts, and the water warms to the room's temperature.
  3. No. It stops cooling when it reaches the room's temperature.
  4. The lid keeps warmth in, so the soup cools more slowly.

Common mistake

"Cold flows into the ice lolly." It is the other way round: warmth flows from the room into the ice lolly. Warmth always goes from the warmer thing to the colder one.

Where it leads