Adventures in home STEM experiments: So many things
A short list of fun STEM stuff you can do at home taken from my Twitter feed
My rate of writing this newsletter slowed down, but this does not mean that I have fewer STEM adventures at my home. Far from that – there is something going on almost daily. Snippets of these activities can be found on my Twitter feed where you can follow me for a regular update.
In the last episode I described how my kid and I grow various crystals at home (see our latest crystal beauty HERE or a crystal that glows under dark light). In this episode I’ll make a review of some of the other fun stuff that has appeared on my Twitter feed. Here are the topics that follow below:
Magnetic balls as an analogue of temperature
Magnetic balls as analogues of crystals
Magnetic balls and why DNA can be so long
How to see magnetic fields
Surprisingly educational magnetic blocks toy
A functioning home-made battery
Cabbage as acidity indicator
Adventures with a Tesla coil
Unusual metals
Making molecules from atoms
Radiation all around us
The mystery of light polarization
Magnetic balls as an analogue of temperature
Electrostatic force between atoms keeps the whole world together, including our body. This is the force between positive and negative electrical charges. Objects around us typically consist of the same number of positive and negative charges, which makes them neutral on our macroscopic scale. But on the level of atoms and molecules, interactions are governed by the electric force.
The world on this scale is weird, albeit not so weird that we could not get a feeling how some things work using simple analogues. For example – temperature.
Temperature that we measure with ordinary thermometers is just a measure of how much energy is stored in the molecular movement (i.e., kinetic energy), where a higher speed of molecules or atoms means a higher temperature. In gas they fly all around; in liquid they slip around each other; in solid they are locked at fixed positions where they vibrate.
During chemical reactions, molecules collide with each other. Most of the time they simply bounce off each other. But sometimes they interact and start to rearrange their atoms. The outcome are new molecules that can be faster or slower, with a part of their energy either taken from or stored into the electric forces within the molecules.
Small magnetic balls are like molecules, with the magnetic force playing the role of electric force. If you play a bit with such magnets, you can notice how interactions between them are simplified analogues of molecular interactions. I made a short movie where I show how the temperature can increase or decrease when the balls (i.e., molecules) move faster or slower.
Magnetic balls as analogues of crystals
The amazing thing about crystals is their flat surfaces that look like someone polished them. But why would atoms and molecules form this? Magnetic balls are great for demonstrating a simplified model of crystal growth that can give the answer.
I wrote a short Twitter thread on this. You can build structured objects with ball magnets and observe how the flat surfaces allow an additional ball to slide unless it gets locked at kinks where other surface balls attract it. This simple approach in explaining the crystal growth is known as the Terrace Ledge Kink model. Depending on the shape of molecules and their interaction, the growth can proceed only into well-defined mathematical shapes. As a part of our home-grown crystal growth, we’ve got crystals in the shape of octahedron and then built an octahedron from magnetic balls. It is much easier to grasp the concept of crystal growth in this way.
Magnetic balls and why DNA can be so long
We have 1000 magnetic balls of 5mm diameter form which we assembled a 5 meters long chain. These very same balls can be rearranged into a flat hexagon of 18 centimeters in diameter. Even more amazing, you can pack them into a 5x5x5 centimeters cube. This mathematical game demonstrates how our DNA can fit into a space just 6 microns across even though it is about 2m long.
How to see magnetic fields
Here is a simple old trick how to see magnetic fields in 3D using baby oil. All you need is a bottle of baby oil and extra-fine steel wool from your local hardware store. In a short thread I explain what to do such that in the end you can observe how the fibers form a 3D shape tracing the magnetic field lines.
Surprisingly educational magnetic blocks toy
While magnets are fun to play with, magnets put on triangles, squares, pentagons, and hexagons are even more fun. The idea that this toy has a potential for STEM fun came after watching a video by Michael Stevens about strictly convex deltahedra. My kid was intrigued how these geometrical shapes were constructed using magnetic blocks. I jumped on this opportunity and bought a bunch of magnetic blocks. And it was a blast!
We spent many hours creating all sort of geometrical shapes. We use various internet sources showing 3D shapes and their (often complicated) names. Platonic polyhedra were the first, but then we moved to their truncated versions. And, of course, we made all eight strictly convex deltahedra.
But there is more! I realized that this spark of interest in 3D geometry can be mixed with educational topics on 3D shapes of molecules. So, we moved to the challenge of building fullerenes from magnetic blocks. Fullerenes are molecules made of carbon atoms connected in such a way that they form a closed or partially closed mesh. It is not easy to build them because they can be really complicated, and their mesh is typically made of deformed hexagons and pentagons. Nonetheless, we managed to put together many types of fullerenes, and then even moved to the mathematics of nanotubes.
A functioning home-made battery
You have probably seen instructions on how to make a battery from lemons. It’s all over the Internet. But this is a useless battery for practical purposes. If you want a serious battery that will run LED lights for many days, then you need to make a battery from copper and zinc.
This battery is called a Daniell cell and it contains copper (II) sulfate (CuSO₄) and a zinc (Zn) electrode. The version we built at home is called a "gravity cell", where the CuSO₄ solution sits in the bottom part of a jar because of its higher density than pure water. Step by step instructions are described in a thread HERE.
The battery works because of the exchange of ions between copper and zinc. Copper has the ability to attract its copper ions more strongly than the zinc's ability to hold its zinc ions. When you close the electric circuit, you enable copper and zinc electrodes to exchange electrons through the wire, while SO₄²⁻ negative ions flow through the liquid.
Cabbage as acidity indicator
One common home experiment definitively worth of playing with is cabbage juice as indicator of acidity or basicity. Acids release H⁺ ions, while bases release OH⁻ ions. Pure water is in between, i.e. neutral on acidity or basicity. In chemistry the scale measuring these ions is called pH. One way of observing pH level of a substance is by mixing it with red cabbage juice. The juice is easy to make: just leave cabbage leaves in a hot water for a while to get a purple-bluish liquid. Then start mixing it with various substances you find at home and observe the change in color.
Adventures with Tesla coils
Tesla coil is a device that produces high-voltage, low-current, high-frequency alternating-current electricity. This type of electricity has some interesting properties – it creates strong oscillating electric field in its vicinity, which results in air ionization (sparks) at sharp corners (called “corona discharge”), and the high-frequency of low-current makes it (almost) safe for handling.
This makes it a great educational toy! You can find two types of Tesla coils. One is so called “plasma ball/globe/lamp” that uses a sealed glass ball filled with a noble gas to make sparks larger and easier to create. The other is pure Tesla coil where you can put various sharp objects on the top of it to observe sparks flying through the air.
We play at home with both of such coils and it is lots of fun. We observed how helium and sodium affect the corona discharge; used a diode and corona discharge to prove that electrons travel with electricity through wires; played with turning on fluorescent lamps without wires; observed the trajectory of sparks in 1000 frames per second video recordings; measured the frequency of electric field changes using oscilloscope; and changed the color of corona discharge using metal ions.
Unusual metals
We use various types of atoms on daily basis that we are not familiar with. Even better, atoms build molecules where the behavior of atoms is different from their pure form. Therefore, exploring the periodic system of elements can be fun.
For example, I purchased small chunks of pure cerium and gadolinium. They are mentals and have interesting properties. With cerium you can make massive sparks when rubbing it against a steel rod because cerium ignites at only 170°C, which can be achieved by simple metal-to-metal friction. (Note: cerium needs to be stored in mineral oil turpentine to avoid deterioration by oxidation).
Gadolinium is interesting because it changes its magnetic properties at room temperature. This is a typical property of metals, but gadolinium does it at 19°C. You can cool gadolinium in cold water and it will be attracted by a magnet, but if you warm it up in a hot water, the magnet will not work on it anymore.
Making molecules from atoms
It is important for kids to understand that everything, including their body and their brain, is made of atoms. The most amazing thing about atoms is how they form molecules that exhibit such a gigantic range of properties. One way to help kids explore and visualize this world of atoms is to give them molecular model kits to play with putting together various models of molecules.
We play at home with this in two ways – either first search for molecules with interesting properties (like nitroglycerin) to make a model or make a molecule and then search the Internet to find if it exists (like oily n-nonacosane).
Radiation all around us
Some time ago I got an old (from the 70’s, I think) Geiger–Müller counter that can detect ionizing radiation. It can detects beta particles (fast electrons) and gamma rays (high energy photons) but can’t detect alpha particles (helium nuclei).
It is quite eye opening to people when they hear “pings” from the counter all the time from seemingly nothing. Ionizing radiation is all around us in very small dosages. But this counter comes with a “control source” – a small metal disk made of strontium-90 (Sr-90). The nucleus of Sr-90 is unstable, and it produces beta particles.
Inspired by the counter making lots of pings when pointed to the control source, I decided to write a thread of fun facts about Sr-90. It is about the explanation of how atomic nuclei decay, about old abandoned Soviet lighthouses in the Arctic, and when and why Sr-90 can be dangerous.
The mystery of light polarization
Light is a very complicated thing. Well, the first problem is to explain what kind of a “thing” it is. But once you settle on some explanation of electromagnetic force wave, here comes a whole new beast – polarization. Polarization is weird and it is the fastest road to dive into quantum physics. This is amazing – all you need is three polarizing filters and you end up in deep mysteries of nature.
But polarization is also fun because you can turn invisible world into visible. Just one linearly polarizing filter and your computer monitor (which emits polarized light) are enough to see mechanical stress in various transparent objects. Or look at the blue sky with such a filter and you will notice differences in brightness.
Moreover, there is also circular polarization. I was motivated to buy a circular polarizer to see one amazing phenomenon – disappearance of color in some spices of beetles! My kid really loves the green rose chafer (Cetonia aurata). It is a beautiful creature with bright metallic colors due to light interference (the topic we covered previously). But, amazingly, the colors disappear if you look at the beetle through a right-circular polarizing filter because the light form beetle is left circularly polarized.
