◆ Science 7 · Term 1 · Week 4

Ten Minutes at Home: Why Sweat Cools You

Nothing to buy, and no equipment at all. Ten minutes and a conversation about something your child already knows happens. It anchors an idea — the particle model — that runs through the next four years of Science and is easy to memorise without believing.

The activity: the back of your hand

minutes: 10 Materials: water, and the back of a hand. A fan or a piece of card is useful and not necessary.

Wet the back of your child's hand with a little water at room temperature.
Ask: <q>Is the water hot or cold?</q> It is neither — it is the same temperature as the room.
Now blow on it, or fan it. Ask: <q>How does it feel?</q> Cold.
Ask the real question: <q>The water was not cold. So where did the cold come from?</q>
Let them think. Do not fill the silence.
If they need a start, ask: <q>What happened to the water that is no longer on your hand?</q>
The answer to work towards: the fastest particles left, so what stayed behind has less energy — and less energy means colder.

Three things to avoid

What usually happens	Instead
Saying <q>the cold air cooled it</q>.	Your breath is warmer than the room. The cooling is caused by water leaving, not by air arriving — which is exactly why the answer is interesting.
Saying particles <q>get bigger</q> when things are heated.	This is the single most common wrong idea in this topic and it is very hard to unlearn. Things expand because their particles move <em>further apart</em>. Each particle is unchanged.
Treating <q>I don't know</q> as the end of the conversation.	Ask <q>what would you need to find out?</q> instead. In Grade 7 the goal is shifting from knowing answers to knowing what a good answer would look like.

Three signs it is working

They say <q>the fastest ones leave</q> about something drying.
They object when somebody says particles grow when heated.
They ask what is in between the particles — and are not satisfied with <q>air</q>.

If you only do one part, do step 4 — <b>the water was not cold, so where did the cold come from?</b> It is a question with a real answer that nothing in everyday language prepares anybody for, and it is the kind of question this year of Science is built on.