Wednesday, June 27, 2012

States of matter

In the previous post I noted how most electricity is generated by the action of turbines transforming mechanical energy into electricity. By far the bulk of those turbines are driven by the motion of steam. Matter exists in three states - solid, liquid and gas. In the solid state the molecules are standing relatively still, in fixed position relative to each other. As such, a solid has both fixed shape and volume. As heat is added, the molecules will vibrate faster and faster, until they reach the point where the energy of the vibration overcomes the forces between the molecules that hold them together, and the molecules slip past each other. This is melting. In the liquid phase, the molecules are still all touching each other, so the volume stays the same, but the shape is variable (that is, when you pour water into a square container, it takes a square shape, but if you pour the same water into a round container it takes a round shape). Now here's the important part for our electricity story: as you add heat to a liquid, eventually the molecules move so quickly they break apart all together and go flying into the air. This is boiling. Since the molecules are not touching in the gas phase, the volume of a gas is variable. As you add heat to a gas, it expands. If you start with liquid water and heat it to boiling, the expanding gas can be directed past a turbine, and the movement of this turbine is what is then used to make electricity. More on the sources of heat tomorrow, but let's give a LEGO representation of the states of matter. After the first and second graders in the Marvelous Multiagers blogger's class had a lesson on the states of matter, some of them created a LEGO version during their playtime. As the teacher describes it, "The big white part is ice. There is a little blue because it's melting a little bit, haha. The big blue part is water. The little white part is a chimney with air coming out of it! We had just talked about how the heating or cooling can change the state of matter, so this really made my day!!". Quick aside - it's pretty much impossible to find a good LEGO image for steam. When you do searches you just come up with train engines and steampunk creations.

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