MEFW Sessions 3 and 4

• 2008 Workshop Main Page
• Non-MEFW links: Main Page, education, and also the map

• MEFW = Measuring Energy Flow Workshop Main Page
• Sessions { 1 and 2}, { 3 and 4 }, { 5 and 6 }, { 7 and planning for 8 }
• Session 8, { 9 and 10 }, { 11 and 12 }
• Session 13, { 14 and 15 }, { 16 and 17 }
• Session 18 and Wrapup for 2007-2008
• MEFW Terminology, Motivation, References
• Project 2061 I, Project 2061 II
• Letter to parents
• March 2008 Data Plots
• Some notes

Introduction

This page covers class sessions 3 and 4 on Measuring Energy Flow. We have established that energy flows and leaks, so the idea here is to start introducing the idea of cycles. Since we have started with electrical circuits the first step is to emphasize circuit on the way to cycle. Also, since we've now struggled with electrical circuits for a couple weeks I'm going to begin introducing terminology, using the water-flow metaphor for an electric circuit.

Summary

The third session was a blast. We divided the six students into two sets of three: A Creek set and a Scientist set. We ran a long pair of wires around the book case and hooked it up to our usual circuit back at the lab table. The Scientists sat at the table and wrote down current measurements every 15 seconds. This became a data table which the students are subsequently to plot. The Creek students added salt to the freshwater supply at various intervals. Since this was out of sight (and in hushed voices) we were effectively simulating a natural environment that changes with time (without telling you what it is doing).

The fourth session was also a qualified success. We walked the 15 minutes to Viele Lake and measured the water conductivity and temperature. We also tested the idea that hydrolysis produces hydrogen and oxygen (the bubbles) by trying to light the water on fire. And last we discussed how to measure the size of the earth, with or without a handy rocket ship.

RF Notes

Setting up the students to create data for themselves is the first step down the pathway to measuring and interpreting environmental factors. I suspect that pH will turn out to be a crucial parameter in local water chemistry so we'll have to get started on understanding it a little bit, sooner than later.

Session 3 What Happened

• Shannon described electric circuits and then put one together
  • It did not work until we screwed in the lightbulb a bit further
  • The kids are getting basic electronics
  • We observed that gravity does not seem to affect how the electrical circuit works
    • (We did this by lifting the lamp up and noticing it didn’t change brightness)
• We prepared to convert Shannon's circuit into our usual Conductivity Testing circuit shown below

• Aside: A pocket weather station was examined: What is it telling us?
  • We will need to discuss these further
• We began a Terminology list
• We took a first look at a Field Mote (to be used for outdoors work later)
• We separated into two teams of 3:
  • Creek: Shannon, Sophie, Liam
  • Scientists: Owen, Matthew, Jack
• We set up a “Creek” on one side of the bookcase (big glass with tap water, salt nearby)
• We set up a long wire back to the scientists at the table
• The Scientists had a power supply, lightbulb, and an ammeter to measure current
• The Scientists practiced recording data readings (current) every 15 seconds
  • Matthew read off the times
  • Jack read off the current reading through the circuit
    • The values he read off were in units of milliamps (from 0 to 120 or so)
    • If the meter was bouncing around he just said “X” for no data
  • Owen wrote the times and values down
  • The Creek waited patiently
• We established that an open circuit gave Zero milliamps

Then we began the experiment

• The Creek had one penny of salt added and stirred in to dissolve in the tap water.
• The Creek received another penny of salt.
• The Creek received a third penny of salt.
• The Creek received a Bunch of salt
• The electrode was removed from the Creek
• The electrode was returned to the Creek
• The Creek received a Bunch of salt
• The Creek received a Bunch of salt

That was the end... now the Scientists had a lot of data which they were charged with plotting. We discussed what happened in the Creek and how to make a plot of the resulting data recorded by the Scientists. The data plot: Horizontal axis is time in 15-second increments, vertical axis is data value (current reading).

Here is the result, with some emphasis added using PowerPoint over the photograph:

• RF did not suggest “connecting” the dots with lines; they did this on their own.
• Note that the addition of lots of salt doesn't change the conductivity; we suppose this is a saturation effect.

Session 4 What Happened

What we did in the Week 4 session:

• Recap for Lucas
• Travel to Lake Viele

It was a blustery day...

...but we stayed warm and set up our equipment on the little dock at one end of the lake. The goal was to measure electrical conductivity of the lake water and temperature as well.

• At the dock the circuit did not work at first...

We often find that getting our basic circuit to work requires jiggling batteries and sometimes even using the voltmeter to see where the problem might be, one step at a time.

• We asked two of our scientists what would happen when the electrodes are put in the lake.

Scientist 1: The lightbulb will not light up because the lake water is fairly pure and so will behave like tap water.

Scientist 2: The lake has minerals and other junk in it and is therefore going to be fairly conductive, so the lightbulb will light up.

• We first put lake water in our glass and checked that, then we placed the electrodes in the lake off the edge of the dock. The third experiment would be to launch the sensors farther out into the lake on a long wire but we'll get to that later.
  • Needed: numbers (temp and current) for lake water in glass, off dock

• A new type of electrode was used today: Pencil-lead graphite, which is very non-corrosive and conducts very well, makes lots and lots of bubbles.

• Intermezzo

The student scientists have listened patiently as RF tells them: "I've heard that the bubbles coming off the electrodes are hydrogen and oxygen. You know, like the Hindenburg was hydrogen and it exploded?"

Today the students asked what would happen if we tried to light the bubbles on fire. RF responded "Let's try it and find out" while producing a lighter. RF had a camera handy and took the following photos of the scientists preparing for this experiment:

• Did the bubbles burst into flame?

Let's just say nobody was injured.

• The sensor package was set into the lake off the dock.

The sensor package consists of an analog thermometer, two graphite electrodes, some rubber bands, and a negatively buoyant screw driver for ballast.

• Did the lightbulb light up?

Here is the bulb when the electrodes were placed in the lake

The lightbulb filament is glowing a little bit; so the lake water has enough "stuff" in it to make the water more conductive than tap water. (Tap water doesn't let enough current through, typically 7 milliamps, to make the bulb glow; in this case we had a little more than 40 milliamps which was enough for a feeble glow.)

• Needed: Numbers for lake versus tap water with this circuit.
• Use these photo:

• Mention Lake Viele in geo context
• During the course of our hour RF kept bringing up the star behind the clouds and the rock behind the clouds.
• RF suggested that the earth is triangular.
• The scientists disagreed, stating instead that the earth is round/spherical.
• RF asked the question: How would you measure how big the earth is?

• • Rob to get a photo of the "clue" mural and recover the sensor package.
  • Rob to write up the deep-lake cast
  • Rob to recover SP

• The following Assignment was given: Draw a picture of something that happened today.

• December 12 (RF hopes) we will measure the size of the earth.

• • Other notes for inclusion
    • Sophie mentions PB's ProblemoftheWeek: Some are easy and some are hard.
    • Review: What have we done so far? Plus terminology.

Week 5 Planning

• Discuss lake in glass versus lake
• Using same setup look at the conductivity of tap water, compare to lake results.
• Do you remember what the day was like (aeolus)? What is that?
• Lazy Susan coriolis, two-pipes convection, wind, pressure.
• Discuss projects in December

No moon for awhile so defer this to 18 days away.