# Energy in Systems: Looking at Subsystems

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## Objective

SWBAT identify and describe energy transfers in subsystems of larger systems.

#### Big Idea

Students build on their understanding of forms and transfers of energy to study. identify and explain subsystems using Rube Goldberg cartoons.

## Getting Started

In this third of three lessons on energy transfers in systems, students turn their attention to the whimsical cartoons of Rube Goldberg. These well known cartoons involve quite ridiculous solutions to a variety of simple everyday problems. Students love to look these images over and study the wild visuals that they contain.

The set up and materials for this lesson are very simple. You will want to obtain copies of a selection of cartoons. I have included a link to a book of Rube Goldberg cartoons below. If you do not own a copy of the text and would rather not purchase one, ask your school library if they have a copy or your local public library. Additionally, a quick Google search of Rube Goldberg cartoons will result in several hits. Click on images and you should see plenty from which to choose and download.

You can manage this in a number of ways. I start by using a sample cartoon that I project on the overhead, walking my class through the steps of a) reading the scenario, b) identifying the systems, c) identifying the energy transfers. Then I give each group of four students a copy of a different cartoon for them to practice with. I use four different cartoons, one for each group.

Prerequisites: types and forms of energy, basic understanding of energy transfers

Materials: Copies of Rube Goldberg cartoons (found online) or here

## Elicit

5 minutes

As review, begin class by asking students to tell you what are the parts of the system.

The system is made up of parts that work together. This system is limited to those working parts that exist within a boundary, in other words where the system begins and ends and the system exists in an environment.

Next ask your students what subsystems might mean. Your class should be able to tell you that it's a system within a system. Then ask for examples of subsystems. For instance the human body's system composed of subsystems, the 11 body systems. A car is a system composed of subsystems. A cell phone is a system composed of subsystems.

## Engage

10 minutes

Ask students if they know who Rube Goldberg is. Give them some background on who he was (1920s, cartoonist, wild, whimsical cartoons of ridiculous solutions to everyday problems).

Project an image of one of Rube Goldberg's cartoons. My example (below) is a cartoon of an automatic garage door opener.

Each of Goldberg's cartoons includes a paragraph or two narration explaining the solution to the problem. Let your students study the image for a moment and then read the explanation to them, pausing at each step of the system. Enjoy the chuckles and laughs that that your students will no doubt have.

Which you have read through the explanation, ask your students if this image contains any subsystems. It may not be obvious to them that cartoon can be broken down into parts, so if they are unable to come up with an example help them through the first system. The systems I have identified in this cartoon may, by no means, be completely accurate, however I have run this by a few physics professors at Boston University who had no conflict with what I have identified.

In the first system the automobile hits a mallet which falls and smashes an exploding cap.

I would then ask my students to identify what types of energy transfers are happening in the system. So for instance, kinetic energy to kinetic energy to gravitational potential to store chemical energy to sound. If your students have not had practice identifying energy transfers refer back to the previous two lessons in this unit for an introduction to identify energy transfers.

Continue to identify the next system and so on and so forth.

With each system identify the different energy transfers. If you happen to see the connection to the systems differently, that's okay. Just isolate and identify the steps and energy transfers for your students.

## Explore

25 minutes

When you have gone over the entire cartoon, instruct the students that they are going to be doing the same activity with a new cartoon. Hand out the cartoon to each group of four students, and as a group have them study and read the narrative before they begin to identify the subsystems. I asked students to identify anywhere between three and six subsystems per cartoon, however they may identify more than that. Along with each subsystem that they identify, they should also look for each energy transfer in that subsystem.

The final part of the activity is to pick one of the subsystems they identify and write out an explanation from the narration of what is happening in that subsystem along with every energy transfer that is occurring.

## Explain

15 minutes

When students are completed with their systems descriptions, have them share with the class their explanation of the cartoon and the systems  they identified. I provide corrections at this time and clarification if I notice that they forgot an energy transfer or made a mistake with an energy transfer.  I really push for clarity and precision at this time since they have had multiple opportunities in previous lessons to work with systems.

In the video below I asked the student to reflect on these ideas in the context of this lesson.

## Evaluate

10 minutes

My expectations for each student are to include the following:

• Circle each system
• Identify the parts of each sub system
• Identify the energy transfers between each part of each subsystem
• Choose one of the subsystems and write a description including energy transfers for that subsystem.

Be sure that these criteria are explicit at the start  of the lesson. This activity take some time and will prove to be challenging for some of your students. You may need to be flexible in interpreting the subsystems as well as helping your students who are struggling to find them.

When students are sharing out their ideas to the class, open up class discussion for feedback to hear what other students might be thinking and allow students to make corrections to their assignment before grading.

## Extend

20 minutes

If you are looking for a more challenging extension to this activity, one that includes a mathematical component  Involving reasoning and making meaning,  have your students do a rough calculation of energy units transferred in the system.

To do this assign them 100 "energy units" for the beginning of the system. At this point energy units can be thought of just as a vague term. We're not thinking of Joules per se. Ask them to guesstimate the number of units that are transformed at each energy transfer in each sub system. So for example, as the car hits the mallet and then the mallet hits exploding cap, how much energy do they think is expended in each of those transfers.

Let them know that they should never get to a negative value so they will need to estimate a small value of energy units within each transfer. The idea here is not to confuse students that we lose energy but each energy transformation reinforces the second law of thermodynamics that as energy transfers we always end up with less energy than the original potential energy we started with. Most of that energy, as we know, can be lost as heat or perhaps as sound and transfers to other parts of the system.

Ask them to write on of the cartoon the numerical values for the energy units in each energy transfer.