# MEFW Session 8

## Introduction

This page covers what happened in Session 8 (January 11, 2008), it covers the Winter Activity Handout (part 1), and it refers to some science education web pages.

Session 8 was unique in that we started to move away from benchtop experiments and into extended discussion of the ideas we've been working on. The students do very well with this particularly as we keep things very interactive. In particular they are asked questions in turn and get a chance to answer before we go to open discussion (although it is a challenge for the other students to maintain restraint sometimes).

We have enough 'workshop context' now that we can easily build bridges (as described in the bridge essay) to depart from familiar territory and wind up back in some other familiar territory. In today's case we began by considering the downhill pathway of water through river channels using the Virtual Earth website. Then we closed up the computer and went off on a (non-sequitur) discussion of forms of energy. This emphasized gravitational potential energy, for example comparing two identical nickels resting at different heights above the ground. At the end of this discussion we returned to the energy lost by a snowflake after it melts at the continental divide and flows downstream to Boulder. This is preparation for another bridge built in session 10.

## The Winter Handout

These dots are stars, part of four constellations visible to the east on winter evenings (Orion, Gemini, Canis Major, Canis Minor). I'll need to scan in the "filled in" version of the chart. The conversation includes a challenge to the students to find these stars in the night sky and notice what colors they are. This in turn will lead up to a spectroscopy lab (cereal boxes and CDs) and the idea that our sun is a star. We all know (because someone told us) that our sun is a star, but I'd like to establish this on a deeper level by means of spectroscopic fingerprints, in itself a type of measurement of energy flow.

## What happened in Session 8

We fired up Virtual Earth and took a tour of Boulder County as if we were all snowflakes that landed one centimeter east of the continental divide. This is coincidentally the western border of Boulder County. In order to get our water molecules mobilized we had the sun come out and melt us so we could flow downhill.

Here are screencaps of the above perspectives... but much better justice is done using the web browser to fly around.

## ...and then session 8 continued...

• Aside: When we looked down at the school we tried looking up and waving but nothing happened on our screen...
• Once we completed our virtual tour we headed over to the empty classroom we use. We're glad Adam is here with us.
• Instructor produced two quarters and we discussed them as sources of energy.
• They have temperature so relative to a freezer they are warmer and have more energy.
• If we throw them they have energy of motion.
• We did not discuss the energy equivalence of matter $\;E = mc^2$.
• We know that when the quarters hit the wall the sound is an example of energy leaking into another form.
• We know that the higher they sit on our hand the more gravitational potential energy they have.
• We know that the one on the table has less potential energy than the one in my hand above the table.
• We know that when they both fall to the ground they have the same potential energy now.
• We know the idea applies to us as well, for example Matthew jumping off of a chair.
• We know that when they are on the floor their energy is not zero. Why?
• Because we could dig a hole in the floor and push the quarters in to fall further and get more energy out of them.
• Just because it takes energy to dig the hole doesn't mean the quarter's potential energy depends on whether or not there is a hole nearby.
• Furthermore we know we are one mile above sea level so we could dig quite a deep hole indeed before we even got that low.
• And sea level is still furthermore waaay above the center of the earth...
• So gravitational potential energy is relative...
• And we can use it up by jumping off of chairs.
• Suppose Matthew jumps off his chair into a 5280 foot hole. That will hurt a lot.
• Or if he jumps out of an airplane at 9000 feet without a chute that will hurt a lot.
• So instead (on a big piece of paper using cartoons) we built him a slide.
• Matthew started at 12,000 feet and slid down the slide all the way to Boulder.
• In this way he was not hurt.
• What is Matthew? Anybody? Sophie: He's a snowflake.
• That's right; so the slide has already been built and it is called Boulder Creek.
• So all that snow falling on the mountains has a lot of potential energy.
• Where does that snow come from? Heat, evaporation, cloud formation, wind, precipitation.
• Ultimately energy from the sun is pushing everything around.
• So the sun is pushing all the water up to the top of the hill, the water slides back down the hill.

The idea of this extended conversation was to cash in on what we've been thinking about and add coherence to our understanding of the water cycle. We will continue this in the next session. The nice closure is that we started with the 3D trip down the slide and wound up back at the same idea from a different direction, that of potential energy stored up from sunlight.

We have questions to revisit next time.

• Matthew's excellent question:Is all the water that was when there was first water still here? Or is there more or less?
• Sophie's question is the earth moving fast or slow? Time to dig out the Universe Song.