# Day 42

Physical Science: Today we wrapped up the ink pen separation. Basically I talked about what they should have gotten for results (after collecting it) and showed them a demo of polarity. I set up two burets, one with water and the other alcohol. These were the mobile phases in the lab. I then used a static charged balloon to show them how polar substances are affected by the presence of an electric field. Sure enough, the water is strongly influenced, but the alcohol is only a little influenced. This was a nice way to segue from the mixture separation lab, which used physical properties of the ink components, to talking about properties of substances.

Chemistry: We continued our discussion on the gas labs that we did. Just a few highlights to hit upon though or I could be here all night.

We developed the other two gas laws that we tested in lab (P v. n) and (P v. T.) The temperature test is a good one to look at. Of course the issue with testing pressure versus temperature in Celsius is that you do not get a directly proportional relationship. That means the the pressure is not an exact multiple of the temperature. This is because at 0 Celsius, the pressure is not zero. So I ask the kids, “What would the temperature have to be in order for the pressure to equal zero?”

Some kids get it right away, others need some push in the right direction. After a couple minutes all groups report a temperature between -300 and -400 Celsius. Then I ask them, “What would have to happen to the gas in order for it to NOT exert a pressure?”

They tell me that the gas would have to stop moving completely; no collisions with the particles, they cannot push on anything. So this means that at their temperature, particle motion would theoretically stop! That’s whn I let them know that a guy named Lord Kelvin figured this out a long time ago, and he found the temperature to be -273 Celsius, which he uses as zero for his new Kelvin scale. From there, plotting results in Kelvin, we get the directly proportional relationship.

So with that we end up with three equations we can use to figure out how changing one variable in a gaseous system will affect another variable:

3 models…for talking about 1 gas…I don’t like it. Why can’t we have one model? That’s when we talk about other possible relationships such as that between gas volume and temperature. We also talk about gas volume and amount of gas. Based on our understanding of particle movement and behaviors, we reason out relationships for those as well:

UGH! 5 MODELS! That’s not better! Or is it? What always appears in the numerator of those ratios? The denominator? What if we smash it together?

1 model. That’s better. But why does it work? It has to do with gases being made of particles, and that those particles are always moving, and that they collide with each other and their containers, right? Maybe we should write those ideas down. They seem to keep popping up.

Physics of Light: Today we actually did the Converging Lens Pre-Lab. Thankfully we got just enough light to make it work.

I love getting out of the classroom and taking a little field trip. After getting those measurements, we went back to the room to complete the data collection for the day. I discussed the theory behind most of this pre-lab in my Day 41 post. What I did not talk about is why we do the two lens combination.

Well, once we get into the actual Converging Lens Lab, we are going to test two lenses for each group. This is to see if there are any differences between lenses. The combination of the lenses is to see if there is some way we can quantitatively combine two lenses working together. This seems like a good idea since anyone who wears glasses, is really utilizing a two-lens system. So why not just get the data and see what happens?!