This activity allows participants to develop an understanding of the relative sizes (volumes) of the planets in the solar system by dividing a big ball of playdough to see how the planets vary in size.
Lesson courtesy of our friends from the Astronomical Society of the Pacific

By dividing a ball of playdough into spheres to scale, students will:

1. visualize the relative volumes of the eight planets of our solar system in addition to the dwarf planet Pluto

• play-doh (three pounds per group)
• plastic knife (one per group)
• wax paper (one sheet per group)
• student worksheets (one set per group)

• planet: a large celestial body, smaller than a star but larger than an asteroid, that does not produce its own light but is illuminated by light from the star around which it revolves.
• volume: the amount of three-dimensional space occupied by an object.

Preparation

This activity works best if the worksheets with the planet names (pages 5 – 7) are placed side-byside on a table, and are arranged to match the order from the Sun. In front of these sheets place the instruction sheet (page 4) and the playdough and plastic knife on the breadboard (or equivalent). Be sure there is enough room in front of the table for the group to work together. It is crucial to have the indicated amount of playdough for each group. If there is less than three pounds, the Pluto piece will be too small to see! We recommend three pounds each and urge you to try the activity for yourself before leading it.

Introduction

For any of these scale model activities, it is useful to start by exploring the notion of models. Referring to playthings, such as dolls or toy cars, can be a useful reference for talking about scale models. For a more thorough exploration of this concept with ideas of how to introduce and discuss it, see the introduction to the Saturn Project.

This activity is designed as a self-guided station activity. Nevertheless, if you choose to do so, it can also be a facilitated activity from the beginning. If you facilitate this activity from the start, begin by asking the participants which planet they think is the largest. For whatever planet they say is the largest (it will most likely be Jupiter), ask them the following question: If we could combine all the planets together into a big ball, what fraction of that ball would the largest planet be? Might it be 1/9 or 1/5, for example? Which is the smallest? Some may say Pluto, even though it is no longer defined as a major planet, but is a dwarf planet. For our purposes, that is fine. We’ve kept it in this activity and it will be dramatically demonstrated just how much smaller it is than the others. End the introduction by telling them they will get a better idea of these relative sizes or volumes after completing this activity.

Note:

If people will be using previously used playdough of various colors, you can reassure participants that mixing colors is fine (after all, many planets are multicolored!).

Procedure

Participants start by reading the instructions handout (page 4), but they should get into working with the playdough as quickly as possible. They should follow the instructions as to how to divide up their playdough, placing the parts in the proper planet boxes (pages 5 – 7). Each time the playdough is divided up and parts are combined to make a planet, be sure participants roll the combined parts around in their hands until the planet has a ball shape.

Wrap-Up

Start by asking the group about some of the discoveries they made regarding the sizes of the planets. Were there any surprises? Ultimately direct the discussion so that they realize the smaller planets (except the dwarf planet Pluto) are the inner planets, while the larger planets are the outer planets. You may also want to note that more than 96% of the combined volume of the planets is in Jupiter and Saturn (approximately 60% in Jupiter and 36% in Saturn). Those giant planets really ARE giants.

• Schatz, Dennis. Family ASTRO Program. Pacific Science Center.
• Astronomical Society of the Pacific, www.astrosociety.org/education.html

Grade Five

Earth Sciences

• 5b. Students know the solar system includes the planet Earth, the Moon, the Sun, eight other planets and their satellites, and smaller objects, such as asteroids and comets.

Materials Sources

Playdough:

Three-pound tubs of Play-DohTM, Crayola DoughTM or other similar modeling clay can be purchased from many craft suppliers. As of this writing, Dick Blick sells tubs of Crayola DoughTM for $7.49 each (www.dickblick.com or (800) 828-4548).

Alternatively, you can make your own dough using the recipe below. The only drawback is that this can grow moldy, so if you plan to do this activity often, it is recommended that you invest in the commercial product.

Kool-Aid™ Playdough Recipe

This recipe makes three pounds of colorful, scented playdough:

• 5 cups of flour
• 1 cup salt
• 4 packages dry unsweetened Kool-Aid™
• 4 cups boiling water
• 6 tablespoons vegetable oil

Mix the dry ingredients together in a bowl. Mix the liquids together and pour them over the dry ingredients. Stir the mixture until it forms a ball (this may take a while — keep stirring). As the mixture cools, it will become less sticky. After the mixture has cooled to room temperature, take it out of the bowl and knead it until it is smooth. Store in ziplockTM bags in the refrigerator until ready to use.Discuss primate threats and conservation with your students.