## Weeks 7 and 8 — Can we record data?

Mrs. Loeffler has been working on getting her students used to making observations and recording them.  In some cases, it’s been going outside and taking pictures.  In others, it’s been recording the classroom temperature, the number of students in class, and the number of HVAC vents that are blowing.  It seems that the students need practice in remembering to make repeated observations, remembering to record what they see, remembering where they wrote them down, and interpreting trends in the data set after multiple data have been observed.  Graphing and table making need some practice too.

We are also starting to talk about the water cycle.  Instead of going straight to the clouds -> upland -> lowland -> waterbody -> evaporate & repeat diagram (we’ll save that for later), Mrs. Loeffler set up an experiment with two model systems: one to model freshwater and the other to model salt water.  The systems consist of a plastic bin, partially filled with water, and a cup, all covered and sealed with plastic wrap.  These models were placed in front of the window, and we are going to try and record observations over the next week.   The students were asked to hypothesize what might happen, and what differences (if any) might occur between the fresh and salt water systems.  In addition to collecting data, they will answer some guided questions to promote thought about what is actually going on in the system.  For those not familiar with this demonstration, we have essentially constructed a solar still, which is a very simple but powerful way to treat water with limited resources.

As part of the experimental setup, we had the students compute how much salt to add to approximate seawater, which is about 3.5% salt.  They had to measure and calculate the volume of the water, convert that volume to weight, and calculate the amount of salt we needed to add to get a 3.5% salt (by weight) solution.  The unit conversions proved to be challenging, and the students will learn more about how and why to do this “dimensional analysis” later on in the semester.