12 Cups: Thermal Energy

Students study the twelve different containers, using reason to deduce their thermal properties.

I gave the middle-schoolers twelve containers — cups, bottles, mugs, etc. — that I found around the classroom and asked them to figure out which one would keep in heat the best. In fact, I actually asked them to rank the containers because we’d just talked and read about thermal energy. This project is intended to have them learn about thermal energy and heat transfer, while discovering the advantages of the scientific method through practice.

Day 1: Observation and Deduction: When I asked them to rank that containers based on what they knew, I’d hoped that they’d discuss the thermal properties of the cups and bottles. And they did this to a certain degree, however, part of their reasoning for the numbers one and two containers, were that these were the ones I used. Indeed, since I use the double walled glass mug with the lid (container number 7) almost every day, while I only use the steel thermos-mug (container number 6) on field trips (see here for example), they reasoned that the glass mug must have better thermal properties.

The twelve containers are labeled with sticky notes, while students' initial assessment of thermal ranking is written on the paper pieces in front of the containers. — The twelve containers are labeled with sticky notes, while students’ initial assessment of thermal ranking is written on the paper pieces in front of the containers.

Day 2: Exploratory Science and Project Organization: On day 2, I asked the class to see how good their ranking of the containers was by actually testing them. Ever since the complex machines project where they had to choose their own objective, they’ve been wanting more independence, so I told them to pretend I was not in the room. I was not going to say or do anything to help, except provide them with a hot plate and a boiling kettle, and keep an eye out for safety.

They got to work quickly. Or at least some of them did while the other half of the class wondered around the room having their own, no-doubt important, conversations. I pulled them all back in after about half and hour to talk about what had happened. But before we discussed anything, I had them write down — pop quiz style — what their procedure was and how it could be improved. The vagueness of some of the answers made it obvious to both to me and the ones who had not been paying attention who’d actually been working on the project.

Of the ones who’d been working in the project, I brought to their attention that they’d not really spent any time planning and trying out a procedure, but they’d just jumped right in, with everyone following the instructions of the one student who they usually look to for leadership. Their procedure, while sound in theory would have benefited from a few small changes — which they did recognize themselves — and the involvement of more of the class. In particular, they were trying to check the temperature of the water every 10 seconds, but it would take a few seconds to unscrew lids, and about 5 additional seconds for the thermometer to equilibrate. They also were restricted because they were all sharing one stopwatch while trying to use multiple thermometers.

Day 3: First Iteration: Now that they’ve had a bit of trial by fire, tomorrow they’ll try their testing again. I’m optimistic that they’ve learned a lot from the second day’s experience, but we’ll see how it turns out.

Following the Energy

As an exercise to transition from ecology to biochemistry in Biology class, I had students follow the energy from the Sun to humans via potatoes. After all, we’ve been putting together food webs, following energy through the food chain, and now I want to start talking about the short and long chained biochemical molecules like glucose and starch, at least at a general level.

Leaves in the forest canopy capturing sunlight. Photosynthesis in action. Because of all the captured (and reflected) sunlight the floor of the forest beneath the canopy is dark with very little undergrowth. Note: these are not potato trees, potatoes tend to grow under the ground, and potato plants are short, bushy herbs.

So, we start with photosynthesis. The leaves of the potato plant capture sunlight and combine water and carbon dioxide to produce glucose with oxygen as a by-product.

$6 H_2O + 6 CO_2 \xrightarrow{light} C_6H_{12}O_6 + 6 O_2$

This reaction takes radiative energy from the Sun, and stores it as chemical energy in the bonds of the glucose molecule.

A glucose molecules with the carbon and oxygen atoms in the ring highlighted. — A glucose molecule that stores the energy from photosynthesis. The carbon and oxygen atoms in the ring are highlighted.

Glucose is a simple sugar, one of the basic carbohydrate molecules (my bio class has not done the testing for carbohydrates yet, but we will soon). Simple carbohydrates are monomers that can be chained together to produce more complex molecules.

Sizable packets of solar energy stored in the chemical bonds of the carbs.

The potato plant chains together a series of glucose molecules it produces by photosynthesis into long chained polymers called starches. Starches are good for long-term storage of the energy because, for one thing, they don’t dissolve in water the way glucose does. (A good metaphor for this might be to have students carry a handful of beads to represent a bunch of glucose molecules versus carrying a string of beads to represent the starch).

Starch molecules form by chaining together glucose molecules. Water is a byproduct.

The large stash of energy consolidated into the starch is an inviting target for animals like humans. We eat things like potatoes to get the starches, only we usually refer to them by their other name, carbs. Carbs are short for complex carbohydrates: since glucose is a simple carbohydrate, a chain of glucoses is called a complex carbohydrate. This is why people on low-carb diets try to avoid foods like potatoes.

For those of us who do eat potatoes, however, we need to break the starches down into their constituent glucose molecules to get the energy. When we eat potatoes, we chew (masticate) them to break down the cell walls and expose the starches to the enzymes, like amylase in our saliva, that breaks apart the long carbohydrate chains into simple glucose molecules. Enzymes, like amylase, are catalysts. Catalysts are substances that accelerate a chemical reaction, but are not used up in the process.

The body extracts these glucose molecules from the digested food in the small intestines. The glucose is absorbed through the small, finger-like, capillary-filled villi that line the small intestines, and gets into the blood plasma. The circulatory system transports the glucose in the plasma to cells throughout the body.

Cells use the glucose for energy by reversing the photosynthesis reaction, in a reaction called respiration:

$C_6H_{12}O_6 + 6 O_2 \xrightarrow{} 6 H_2O + 6 CO_2 + Energy$

So the cells use respiration to liberate the energy the potato plant captured from the Sun.

Teachers’ Note

I very much liked how this exercise worked. Trying to follow the energy through the plant and human, while using as much biological vocabulary as possible, really worked to integrate our discussions of anatomy and ecology, and helped introduce biochemistry. I think I’ll try other exercises like this, where students try to follow a specific atom through the human body or through the environment (as we study global biogeochemical cycles). It might also be useful to use this as an example of how isotopic tracers work.

Nuclear vs. Chemical Energy

This curious video advocates for a new type of nuclear reactor (that runs on thorium) over traditional uranium reactors and chemical fuels. In doing so it gives a useful, but quick, explanation of how energy is produced from these sources.

The Geology of Oil Traps Activity

The following are my notes for the exercise that resulted in the Oil Traps and Deltas in the Sandbox post.

Trapping Oil

Crude oil is extracted from layers of sand that can be deep beneath the land surface, but it was not created there. Oil comes from organic material, dead plants and animals, that sink to the bottom of the ocean or large lakes. Since organic material is not very dense, it only reaches the bottom of ocean in calm places where there are not a lot of currents or waves that can mix it back into the water. In these calm places, other very small particles like clay can also settle down.

Formation-of-oil-traps — Figure 1. Formation of sandstone (reservoir) and shale (source bed).

Over time, millions of years, this material gets buried beneath other sediments, compressing it and heating it up. Together the organic material and the clay form a type of sedimentary rock called shale. As the shale gets buried deeper and deeper and it gets hotter and hotter, and the organic matter gets cooked which causes it to release the chemical we know as natural gas (methane) and the mixture of organic chemicals we call crude oil (see the formation of oil and natural gas).

Formation-of-oil-traps2 — Figure 2. The trapping of oil and natural gas by a fault.

Shale beds tend to be pretty tightly packed, and they slowly release the oil and natural gas into the layers of sediment around them. If these layers are made of sandstone, where there is much more space for fluids to move between the grains of sand, the hydrocarbons will flow along the beds until they are trapped (Figure 2).

In this exercise, we will use the wave tank to simulate the formation of the geologic layers that produce oil.

Materials

Wave tank
Play sand (10x 20kg bags)
Colored sand (2 bags)

Observations

For your observations, you will sketch what happens to the delta in the tank every time something significant changes.

Procedure

Fill the upper half of the tank with sand leaving the lower half empty.
Fill the empty part with water until it starts to overflow at the lower outlet.
Move the hose to the higher end so that it creates a stream and washes sand down to the bottom end — observe the formation of the delta.
Observe how the delta builds out (progrades) into the water.
After about 10 minutes dump the colored sand into the stream and let it be transported onto the delta.
After most of the colored sand has been transported, raise the outlet so that the water level in the tank rises to the higher level. — Note how the delta forms at a new place.
After about 10 more minutes dump another set of colored sand and allow it to be deposited on the delta.
Now lower the outlet to the original, low level and observe what happens.
After about 10 minutes, turn off the hose and drain all of the water from the tank.
When the tank is dry, use the shovel to excavate a trench down the middle of the sand tank to expose the cross-section of the delta.

Analysis

1. How did changing the water level affect the formation of the delta.

-
-
-
-
-
-

2. When you excavated the trench, did you observe the layers of different colored sand in the delta? Draw a diagram showing what you observed. Describe what you observed here.

-
-
-
-
-
-

3. Was this a realistic simulation of the way oil reservoirs are formed. Please describe all of the things you think are accurate, and all of the things you think are not realistic?

-
-
-
-
-
-

The Formation of Oil and Natural Gas

When organic material is buried it is compressed and “cooked” because the deeper you go beneath the surface of the earth the hotter it gets. This causes the breakdown of the organic matter and the production natural gas and oil. The stages of decomposition are:

Diagenesis:

Decomposition of biological material produces methane gas. At slightly higher temperatures and pressures the organic matter is converted to kerogen – an unorganized (amorphous) material of carbon, hydrogen, and oxygen.

Catagenesis:

At higher temperatures and pressures kerogen is altered and the majority of crude oil is formed. During this phase and the next, the larger molecules break down into simpler molecules such as octane and propane (a process called cracking).

Metagenesis:

In the final stage of alteration (at higher temperatures and pressures) of kerogen and crude oil, natural gas (mostly methane) is produced and residual carbon is left in the source rock.

A Model Solar Water Heater

One of the middle-school projects is to build a little solar water heater. By simply pumping water through a black tube that’s sitting in the sun, you can raise the temperature of the water by about 15°C in about 15 minutes.

Next year I want to try building an actual solar water heater, similar to the passive air heater my students built two years ago, with the tubing in a greenhouse box to see just how efficient we can make it.

How Black? 99.7% Black

One of my students asked, “How black can you get?” I didn’t know the answer; however, serendipitously, I ran into this article last night. Researchers in Rochester, NY have created a solar cell that absorbs 99.7% of incoming light, which means that it has an albedo (reflectivity) of just 0.3%. Since solar cells create energy by absorbing light, the more light it can absorb — the blacker the solar cell — the more efficient the solar cell is likely to be.

Nearby Coal Plant’s Leaking Coal Ash Pond

View Ameren’s Coal Power Plant in a larger map

Jeffery Tomich had a good article last month on the leakage from the coal ash pond at a coal burning power plant near to our school. While the leakage appears to pose no real risk to us, it is a serious environmental issue at a local site that a number of students drive by on the way to school.

I’ve annotated the following excerpt from the article based on the questions my students asked when we talked about the it.

Since Since 1992, a coal ash pond next to the Ameren power plant here has been … hemorrhaging up to 35 gallons a minute [into the local groundwater].
…
At many [other] sites, trace metals in coal ash including lead, mercury, arsenic and selenium have been found in groundwater at levels that exceed drinking water standards.
…
In 2007, a U.S. Environmental Protection Agency report identified 63 sites in 26 states where the water was contaminated by heavy metals from coal ash dumps. That was more than a year before an estimated 5.4 million cubic yards of coal ash sludge escaped an impoundment in Kingston, Tenn. The sludge spread across 300 acres, and 3 million cubic yards spilled into a river.
…
The waste is created from burning coal to create electricity. At Labadie’s ash ponds, it’s composed of fly ash, a fine, talc-like powder that’s captured by filters in the plant’s stacks to reduce pollutants released into the air, and bottom ash, a coarser material that falls to the bottom of coal boilers.
…
a report prepared by Robert Criss, a Washington University professor, identified several dozen private wells along the bluffs near Labadie Bottoms that could be at risk of contamination. Contaminants could infiltrate from shallow alluvial soils to the deeper Ozark aquifer [(see also USGS, 2009)] tapped by residents for drinking water, according to the report.
…
Ameren believes the leaks don’t pose an environmental threat. But because of ongoing concerns, and because the EPA has asked the utility to monitor them, Ameren will make repairs to the ash pond by the end of the year

— Tomich (2011): Leaks from Ameren toxic waste pond in Labadie stir fears in St. Louis Today.

More information from the local environmental group, Labadie Environmental Organization:

The ash overflow in Tennessee: see Dewan, 2008.