Atoms, melting and freezing

Sept. 29, 2019 Code on Github


The aim of this experiment was to introduce our five year old to the idea of atoms, and states of matter. Our two year old also watched. It was a very simple and not very exciting experiment, but I used it to ask some questions to see what they knew already. I also made some simulations to help illustrate the idea of atoms, and give the five year old something more tangible to experiment with (and also because I wanted to make them).

Melting ice

What you'll need:

  • Two ice cubes
  • Two small dishes
  • A fridge

What to do:

  • Put an ice cube in each dish
  • Put one dish in the fridge
  • Put the other dish on the radiator (or in the sun)
  • Wait for 15 minutes to an hour and compare them


After setting up the experiment (and giving both children an ice cube to eat, because that's what they wanted to do with the ice cubes), I asked some questions, to get them to make some hypotheses.

What is ice?

It's a type of rock, but when it melts it turns to water.

What will happen to the ice on the radiator

It will melt.

Which ice cube will melt faster?

The one on the radiator will melt first.


Because the radiator is hot.

Why will it melt?

Because it's too hot.

What will happen to the ice in the fridge

It will stay frozen.

What does frozen mean?


I probably could have probed more, but they were getting a bit bored by then, and I think I'd reached the limits of their understanding. Perhaps unsurprisingly, even our two year old understood that the ice would melt.


A week or two after the experiment, I finally got some simulations working and showed the five year old. I have to say he was way more excited than I expected.

I started by showing him the still images and saying that everything was was made of atoms, hard things like the table, wet things like water, and even the air around us. Atoms are like very very tiny balls that bounce around. He then checked that I really meant everything:

Even this [the computer]? Even the sky? Even us? Even buttons? Even eyes [pointing the googly eyes on a toy]?


This simulation shows atoms in a solid, like in the ice cube. They are neatly arranged and don't move much (they bounce around to start with because the initial spacing between the atoms isn't quite right).


This one is more interesting. It starts with a something like an ice cube, but the walls of the simulation are warmer. So, the atoms move more and the "ice" melts, flows and fills the bottom of the container. The atoms move about more, but still mostly stay joined together. Over time, the red and the blue atoms become mixed up.


By this point my five year old was dying to try the third and final box. This one also starts out with a solid block, but now the container is a lot hotter, so the atoms move a lot faster. They quickly fly away from one another and fill the container. Within a few seconds, the red and blue atoms are completely mixed.

So, despite a pretty boring experiment, it went pretty well. Hopefully it should lead on nicely to an experiment we've already done dropping food colouring into hot and cold water. I'd like to try that again, this time with simulation to show what's happening at a molecular level.

Comments (1)

Hope on Nov. 28, 2019, 5:05 p.m.

this was good explaining. Could you do one for why ice cubes can melt in a fridge?

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