The Sankey Diagram - Energy Transformation Visuals

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Students research the concept of the Sankey Diagram and create their own diagram for a topic of interest.

Big Idea

The total energy of a system is constant as the energy changes from one form to another.


Knowledge is stored in two forms: linguistic and visual. The more students use both forms in the classroom, the more opportunity they have to succeed. For homework, students were given the Sankey Diagram sheet during the previous class and were asked to apply the concept of energy conservation as it applies to a Sankey Diagram (a visual representation of how something flows through a devise or process). A Google Image search on "simple sankey diagrams" yields results like this one. Examining the images one can see that a Sankey Diagram is a display of how input energy divides into other energies as the energy progresses through a system. This makes a Sankey Diagram a great visual application of the conservation of energy. 

In completing the tasks today, students apply CCSS Math Practice 2: Reason abstractly and quantitatively as well as NGSS Science Practice 5 Using mathematics and computational thinking. Students also develop and use models which is an application of Science Practice 2, they create their own Sankey Diagram which involves Science Practice 8: Obtaining, evaluating, and communicating information. All of this is in the context of NGSS performance standard HS-PS3-1: Create a computational model to calculate the change in the energy of one component in a system when the change in energy of the other component(s) and energy flows in and out of the system are known.


Sankey Quiz

5 minutes

The purpose of today's assignment is to apply the concept of a Sankey Diagram to a situation that the students choose. For homework, students were to teach themselves about Sankey Diagrams. There are different ways to use homework: sometimes I assess student understanding of the content with a quiz, sometimes I collect the homework and grade it for correctness and other times I simply check to see that students have completed the assignment. Today, I assess for student understanding with a Sankey Diagram quiz. If they complete the homework, they should ace the quiz. On the first slide of the Sankey Diagrams power point is a picture of my phones battery usage. Students have two minutes to create a Sankey Diagram on a blank piece of paper, which I collect for grading. While students take the quiz, I collect the homework sheet in order to share exemplary Sankey Diagrams that students created.


Sankey Share

5 minutes

After the quiz, I use my document camera to share some of the exemplary Sankey Diagrams students created for homework (download this PDF to see the entire document as the preview only shows the first page). When one does a Google search for Sankey Diagrams, it is clear to me that the internal combustion engine must be one of the first hits as that is the most popular example provided.

For the students who did the homework assignment, their applications of the Sankey Diagram are appropriate. They understand the concept and can apply it well. One of my favorite examples from the student work is a diagram of how the milk in their house is used. Clever application. 

This activity has students view a variety of Sankey Diagram examples that their peers made. The purpose is to activate their thinking for the next task, which is to create a Sankey with several outputs.

Sankey Creation

30 minutes

Practice increases mastery of a topic, so I have students spend the next 30 minutes to create a new and more involved Sankey Diagram. With the second slide of the Sankey Diagrams power point displayed, students learn that their diagram must have at least 5 outputs and the numbers they use must be accurate with numbers they cite from the internet or a textbook. I provide classroom textbooks and computers for students to use, however most students prefer to use their smart phones.  I instruct students to break into groups of 2 to create a new diagram. When students work together, it yields a positive effect on overall learning and allows students to bounce ideas off of each other.

Groups start by brainstorming ideas for their diagram. I hear students contemplate a variety of objects and processes for which they could make a Sankey Diagram. Most groups spend the first 10 minutes in this discussion. Once they settle on something, they spend 5-10 minutes searching the internet for reliable sources to collect their numbers. Then the last 10-15 minutes are spent on making the diagram. The reflection shows the excellent work produced. 


Closure with Bendini Motor

10 minutes

For the closure, I show a video where the Mythbusters test out some free-energy devices (2004 - Episode 24 - "Ming Dynasty Astronaut"). One of them is a Bendini motor where a spinning flywheel has magnets attached to it. The magnets are placed near coils of wire and the concept it that the spinning flywheel induces a current in the wire and that current is fed into an electric motor that is powering the flywheel. Of course, when put to the test, the Bendini motor quickly runs out of power and the concept of "free-energy" is busted. 

I challenge the students to make a Sankey Diagram of a Bendini motor and I tell them that the outputs are friction and induced current. I want to see if students can devise a Sankey Diagram for such a situation. I walk the class to see what the students come up with. 

After a few minutes, I display the final slide of the Sankey Diagrams power point that shows my interpretation of a Bendini motor Sankey diagram. Many of the students have devised a similar picture. 

Before students leave, I give them the E=mc2 Homework sheet. This assignment has students research the meaning of Albert Einstein's most famous of equations, E=mc^2. This gives students the background needed in order to participates in the next class activities.