I love when I can take science activities for kids that I’ve done in older grades and bring it into kindergarten and it be equally well received. In science class, we discussed the properties of water and how water molecules move differently depending on the temperature of the water. Although this is easy to tell kids, it is even better to show them!
This experiment is easy to do and requires very few materials. Start with 2 large glass (heat safe) containers. Add ice cold water to one container. I typically leave a few ice cubes in the water to show kids how cold it is. To the other container, add boiling hot water. (Make sure kids are not close enough to touch the containers or be near the boiling water.)
Next, I asked kids what they thought would happen if I added a drop of food colouring to each jar. The first answers, were of course, that the water would change colour. I asked if they thought there would be any difference between the two jars? Generally, kids figured that since they were both just water, that the temperature wouldn’t make a difference.
As soon as I added the food colouring they noticed the difference! In the cold water, the food colouring moved very slowly and took a long time to mix in. In the hot water, the drop of food colouring spread out quickly and changed the colour of the water at a much faster speed than the cold water. There is something mesmerizing about watching food colouring mix into water. So it is always interesting to watch, but more importantly the experiment very clearly demonstrates that the molecules are behaving differently in the 2 jars.
As an extension, since my kindergarten class is learning about colour mixing I added some blue to the jars to make purple. There’s something really calming, yet exciting about watching the food colouring disperse through the water. It led to great discussion as to why there was the difference between the waters that otherwise look identical.
The molecules in the hot water are moving quickly and therefore bouncing off of each other. So when I added the food colouring, the molecules move the food colouring around fast with it – which we see as mixing. In the cold, water, however, the molecules are moving slowly. Therefore, when I add the food colouring, it moves slowly with the water molecules. To further the idea, the molecules in ice barely move at all. Having children move their bodies like the molecules is a great gross motor activity too!