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In Term Two and Three we have discussed using color coding to better visualize heat and change. Primary colors are used to signify major states. Yellow is normal, red is hot or high, blue is cold or low. The secondary colors of Orange, to show warm and Green, to show cool are used, while purple is not used in this visual code.


Below are some discussions used to illustrate how these colors can be used to illustrate states and change.


This exchange originally took place in the ETF discussion board at etf.mos.org If you are an ETF teacher, you can get access by making an account on the system.


If you are a student, you can add to the discussion through your wiki or in conversation and visual projects in class and out in the world. Try to find some scenarios that this color coding scheme can be applied to.


This is not a standard system, but it is one that makes a lot of basic sense without being simplistic.


Here is an audio explanation of the color system: http://feeds.feedburner.com/~r/FussingWithStuffPodcast/~3/9036766/041-joeltalksenergy.mp3

Original message:

I am looking for a good way to demo the heat color coding. My students are convinced that heat can only go towards cold. My understanding of this from the etf materials is that the difference drives the change. So according to the etf, heat can go towards and affect cold, and cold can go towards and affect heat. A big block of ice in the room can lower the temperature, and a hot drink on a cold day can warm me up. Insulation or lack of it can slow or speed up the process.


So how do I get this across with confidence?


In Project 2 students learned the scale of colors from red, above normal, to blue, below normal. They can sketch and color code both thermal scenarios.


Color coding should help students visualize and talk about what is happening at different snapshots in time. When they are really familiar, they may be able to talk about situations without even sketching and coloring:


1. Heat in yellow, normal temperature air flows to blue ice, melting some. The air and the melt water both get a tinge of green, while the ice remains blue. Room is cooler; ice maintains temperature, but there is less of it. Melt water is warmer than the ice, but still colder than the air, so heat in the air continues to flow to the melt water. All continues until the difference disappears, i.e. ice is gone, and air and melt water are the same color, same temperature.


2. Heat in red drink flows to your body which might be orange compared to green or blue air temperature. Your exterior feels cold because you are losing heat to the cold air, but the hotter drink transfers heat to your core, giving an internal feeling of warmth.


The big benefit in color coding for EtF is that you can ask students to code and then use simple questions like 'Why did you use orange there?" to gauge their grasp of concepts. Coding makes it easier to get everyone into the discussion. It provides a way for students to work out explanations of change in thermal systems, with which they are most familiar, and then apply the same technique later, as projects progress, to explain and even predict less familiar unifying concepts for pressure and electrical differences. -Lee

One thing I didn't point out is a misinterpretation RE: "So according to the etf, heat can go towards and affect cold, and cold can go towards and affect heat." We don't profess the second part. The ice situation confuses because it is Normal (room) temp (Yellow) moving to Below Normal (ice) temp (Blue), but that is still heat moving in the direction of higher concentration to lower.

One other point is that when students code the boat, they will need to have separate sketches and color combinations for temperature and pressure for any given snapshot in time...the colors will not be the same. For example, from the onset of heating the water in the boiler goes to (Red) first, but pressure could still be yellow to orange until phase change to vapor occurs and causes pressure to go Red.

- Lee

Hi everybody,


I wrote the following offline, before these last few emails came in. As

an addendum to the below, I would add that the term "heat" is a very

problematic word in physics. Officially, it is defined as energy being

transferred from a higher temperature to lower temperature body. By

that definition, heat is a process, perhaps better stated as "heating,"

and can't be stored in a body. But we can avoid the word heat, and only

talk about temperature differences and energy transfers, and not step

on the toes of AP physics.


1) We say that energy always transfers from a HIGHER TEMPERATURE to a

LOWER TEMPERATURE, and we color-code TEMPERATURES. Temperature is

something we measure using a thermometer or some other instrument.


2) While temperature is related to "hot" and "cold," those are the

names we give to FEELINGS we humans perceive. The idea that "heat can

go towards and affect cold, and cold can go towards and affect heat,"

might make sense in terms of our feelings, but it can be confusing for

understanding the scientific model. If instead we keep temperature in

mind, then something that feels warm or hot is at above-normal

temperature, and something that feels cool or cold is at below-normal



3) Once we're using the colors exclusively for temperature, then the

direction of energy transfer becomes clearer. A red-to-yellow

difference (say hot chocolate in room temperature) causes energy to

flow from the "hot" object to the "normal" object. The hot chocolate

cools down as the temperature difference disappears until both the room

air and the drink end up at the same temperature.

In the case of an ice cube, which we could color-code "below-normal"

blue, energy will transfer from the room-temperature air (yellow) to

the ice cube (blue). As Lee mentioned, it is a normal-to-below-normal

difference, which can be confusing at first. But energy still transfers

from higher to lower temperature.


4) Ice cubes can be even more confusing because, although we take them

for granted, they are special things. If we get the ice cube from the

freezer, how was the ice cube created? We plugged the freezer into the

electrical outlet, and the freezer uses energy transferred through the

wires to create a temperature difference between the inside and outside

of the freezer. We don't have to worry right now about HOW the freezer

works (it's kind of like a heat engine run in reverse), but remembering

that "it takes a difference to make a difference," the temperature

difference created by the freezer between the normal room temperature

surrounding and the below-normal inside of the freezer allows energy to

flow from yellow (normal temperature) water to cold air (below normal)

in the freezer. The water temperature lowers enough to cause it to

freeze into ice.

When we then take the ice out of the freezer and leave it in a room,

the room will cool as the ice melts, but the cooling is the end result

of the difference created by the freezer to make the ice in the first

place. And the freezer runs because of a voltage difference, itself

created somewhere else, usually a power plant run by a temperature

difference created by burning fuel to run a heat engine. That's the big



5) Returning to the boat, a temperature difference between the burning

candle (red) and the room-temperature water in the boiler (yellow)

causes the water to get hot and boil. The boiling water turns into a

gas, and the gas takes up more space and therefore increases the

pressure inside the boiler. This pressure difference between the gas in

the boiler (red) and the atmosphere (yellow) causes water to flow out

of the boat. That's the somewhat static picture. The dynamic picture

includes another moment color-coded later, when the pressure in the

boiler drops below atmospheric pressure (blue), and the pressure

difference (atmospheric yellow to below-normal blue) causes water to

flow back into the boiler. Again, this is the less intuitive

normal-to-below-normal difference, but this time it's a pressure

difference causing a fluid flow.

The inflow of fresh water is again normal yellow temperature, and it

helps to cool the engine down. This cooling function of the water is a

KEY POINT we want students to appreciate. If the engine didn't cool

down, it wouldn't be able to run for another cycle. It helps to explain

why car exhaust is warm, why power plants have big cooling towers with

hot steam coming out of them, and why engines cannot use all of the

energy that we put into them, inherently limiting their efficiency.


This fairly complex interplay between temperature and pressure

differences in the engine, which also change over time, can be

difficult to get a grasp on, both for teachers and students. But

hopefully with some practice, you'll start to be able to visualize the

relationship. It doesn't have to be perfect -- in fact, it can't be,

since it's just a qualitative way of thinking of what's going on. But

it can be useful, if for no other reason than giving some tools and a

language for discussing what people think is happening.


Hope this helps. Write back with further questions.



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