In the first part (here) of liquids we looked at buoyancy, surface tension, density and viscosity. We continued with these concepts even further. I like to do several experiments on the same topics spread over time. The reason for this is the way our brains work. If we hear a concept only once, and even if we get it and believe to have understood it, if it remains unused, our brains are hardwired to forget it. So spacing repetition of concepts and bringing them up in various experiments is a way to move the concept out of the working memory into vocabulary, so it is no longer just remembered but used so frequently that it is a part of everyday language.
Also, in our house at least, daughter is very interested in the actual doing and far less in the explanation of why it works. So if we do several experiments and I prattle on while she is focused on the actual doing of the experiment, more information is bound to seep through than if we just do something once.
First we built some boats. I ripped out some tinfoil and gave a piece to my five year old daughter and took a piece myself (see images below). Then we built some boats. My boat is on the left and daughters is on the right in the top left side of the image. Mine had sturdier sides and daughters’ had a better bottom. Then we tested to see if they floated (buoyancy). Finally daughter wanted to see if they would float with dublos inside and indeed they did, until there were enough of them for daughters ship to capsize and sink. While we were doing this, I explained to her that in order for the ship to float, it needs to be less dense than water, so it will remain on top of the water. Water will work itself under anything less dense than itself as gravity pulls on it harder. Adding in dublos added weight, but still the overall density is less dense (and therefore weights less) than water. Gravity pulls on everything, but it pulls more on the things with more stuff in them (more dense) and less on things with less stuff (less dense). This is why ships float.
Previously we had studied how to stack solid objects. At that point she thought that it would be impossible to stack liquids. First we prepared the liquids. We created a sugar water solution that was saturated with sugar (see this post for more information on saturation). I opted for salt, she wanted sugar, so sugar it was. Last time we made this, I just dumped the allotted amount of sugar in all at once, this time we added sugar a bit at a time until saturation was reached (no more sugar will dissolve). In the image below you can see the undissolved sugar crystals in the bottom. We left this to cool as we went swimming. After we gathered the rest of the liquids: honey (or syrup), sugar water, water (can be coloured) and oil. I asked daughter to mix these and order them from the most viscous to the least viscous. She mixed and studied each and ordered them. Juice was the least viscous and honey the most. Then I poured the liquids in a clear glass in the order from the most viscous to the least so honey, sugar water solution, juice and oil. So it is possible to stack fluids if two conditions are met: 1. one has a container. Liquids need one. 2. The liquids have different viscosities. Daughter wanted to mix our liquids up so I let her. The juice largely mixed with the sugar water and a little bit of the honey, but some honey remained on the bottom and the oil refused to be mixed at all.
If you try these experiments at home and your child asks questions, please let me know what they ask in the comment section so I can further develop these instructions. If you have questions about these experiments or instructions, leave me a comment and I will answer and also improve these instructions. Also, please remember like and share if you find this useful.
Copyright text and images: Satu Korhonen. You are free to try these experiments out, use them in your teaching. But instead of copying the text or images, link back to this page.