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Three Principles Play

Background: Dr. Art's Guide to Science, Chapters 7, 8, and 9.

The book's three systems principles help us understand how our planet works. This one-scene play shows the three principles in action, and provides another way to learn and understand them.

Equipment and Supplies:
Something to represent the sun; a cow costume; a plant costume; a shopping bag labeled "SUGAR" or somehow conveying that idea; one black balloon; three yellow balloons; a safety pin.

10 minutes


  1. Have three volunteers stand next to each other representing the sun, a plant and a cow. Explain to them and to the spectators that they will do the same scene three times. The first time you will show them their actions and say their words for them. The second time they will do their actions and say their lines. The third time they will do their actions silently, and the audience will say their lines.

  2. Begin with the sun.
    Sun's Words: I am the sun. I am the main source of energy for planet Earth.
    Sun's Action: Give a yellow balloon to the plant.

  3. Next say the plant's words and help it do its actions.
    Plant's Words: I am a plant. I take energy from the sun and carbon dioxide from the air and I make sugar.
    Plant's Action: Take the yellow balloon it got from the sun and a black balloon and put them inside the sugar shopping bag.

  4. Next say the cow's words and help it do its actions.
    Cow's Words: I am a cow. I eat the plant. I breathe the carbon dioxide back into the atmosphere. I use the energy in sugar to walk, eat, be warm, moo, mate, be a cow. All that energy eventually changes to heat and leaves the planet.
    Cow's Action: Chew on the plant's arm. Take the black balloon out of the shopping bag and give it to the plant. Take the yellow balloon and, pointing into the distance, pop it with the safety pin.

  5. After doing the scene three times, ask the audience how many black balloons were used. (one) How many black balloons would be used if we did the scene ten more times? (still just one) Explain that this illustrates that Earth is a closed system for matter, summarized by the phrase "matter cycles." The same atoms go round and round.

  6. Ask the audience how many yellow balloons were used. (three) How many yellow balloons would be used if we did the scene ten more times? (ten more) Explain that this illustrates that Earth is an open system for energy, summarized by the phrase "energy flows." Earth is a solar planet, receiving energy from the sun. That energy does not stay here; it leaves the Earth system as heat.

  7. Point out that the plant and cow depend on each other. Explain that their relationship helps illustrate that Earth is a networked system for life, summarized by the phrase "life webs." Earth is unique in the solar system in featuring a global web of life.