We’ve got a new science topic today! The next few science posts will all relate to heat. These lessons were made for 3rd and 4th graders, but I think they could be used for older kids as well. Some of these topics are pretty challenging. This is kind of a first pass for young kids, but older kids may find these demonstrations and explanations helpful for a deeper level of understanding.
Sources of Heat
The main takeaway of this is that heat is a form of energy. Heat results when electrons, atoms, or molecules move past or bounce off each other. This is typically discussed in physics classes. Heat also results from exothermic reactions. These reactions are discussed in chemistry. I brought these points home at the end of the class, but I started it with concrete examples. First, I reviewed the periodic table/elements, atoms, and molecules. I stressed that atoms want to be electrically neutral (same number of protons and electrons), but they also want to have a full outer electron shell. This leads to atoms forming molecules to share electrons with other atoms. This allows them to be charge neutral and to have filled electron shells. All of these sections have slides with cartoons to help explain these concepts.
I had the kids move their hands past each other several times without their hands touching, and asked if their hands felt warm or cold. Then I had the kids rub their hands together, and asked how their hands felt. I explained that the surfaces of things on a microscopic level are not smooth. You need to do work to move the molecules past each other. When the surfaces move past each other it results in heat. I had a clear container of ping pong balls so the kids could see that you would go through peaks and valleys if you ran your fingers along the round, stacked ping pong balls.
The metal atoms in a wire share their outer electrons in one big cloud. Electrons are introduced into the wire (electricity) and move along it. However, the electrons do not flow through like water running through a pipe. They bounce around on the atoms in the wire. These collisions result in heat. To demonstrate this, I had the kids sit in a group and started rolling ping pong balls through them, and had them continue to roll them through to the other side. The ping pong balls bounced around through the group, similar to the electrons bouncing around in a metal that conducts electricity.
I showed the kids a picture of the fire triangle. I told them that enough oxygen is present in the air to make combustion happen. I showed them the molecules with a chemical reaction for methane (CH4) + oxygen (O2) –> carbon dioxide (CO2) + water (H2O) + energy as an example of a combustion reaction. I explained that when heat is added the bonds in the methane and oxygen, the molecules break and then new bonds form to make carbon dioxide and water. Energy is released in this reaction in the form of fire. I made a coloring sheet for the kids about the fire triangle and fire safety. We went through not leaving cooking or candles unattended, and what safety measures you should take when you make a camp fire.
I also explained that different elements react differently. Hydrogen burns, but helium does not. I asked the kids if they had ever seen a helium balloon pop, and if they ever saw one pop because it touched a candle or a camp fire. Then I had them compare that to what they saw in this video (1:30-6:55) of hydrogen filled balloons exposed to fire. Helium is a noble gas. It has a full outer electron shell and it’s charges are balanced. However, hydrogen does not have a full electron shell and it is very reactive.
You need heat to start a combustion reaction with oxygen, but not with flourine. This is because flourine only needs one electron to fill it’s outer electron shell, and it is very reactive, as you can see here (2:30-5:45).
Nuclear Fusion in the Sun
The sun is a star. Like all stars, it radiates heat. Stars have a life cycle. When the mass of a star is pulled in by gravity, it creates enough force for nuclear fusion to commence. Stars convert hydrogen atoms into helium for most of their life. This reaction creates a lot of energy that pushes against the gravity. This is called a dynamic equilibrium. When a very massive star uses up most of it’s hydrogen it will start to create other more massive elements towards the end of their life. You can see those elements listed above. All of these reactions result in energy, except for the production of iron. When iron is made the star collapses in on itself. This can result in a supernova and/or the creation of a black hole. All the other more massive elements found in nature are created when the star explodes.