Session 4: Planet Sizes

In this session we will be exploring the relationship between length, area, and volume.  The primary activity is the construct, using play dough, models of the planets which are the correct relative sizes.  It requires three pounds of dough and takes about 45-60 minutes to complete.

"Size" is a tricky word.  Jupiter's diameter is only about 11 times that of Earth.  So it's 11 times bigger, right?  Well, sort of.

As the children have learned, area looks like length times width.  In the case of a sphere, this turns into something proportional to the square of the diameter of the planet. So Jupiter's nearly 11 times larger diameter gives it about 120 times the "surface" area (Jupiter doesn't really have a well-defined surface like Earth).

Ah, but when we look at three dimensional objects, we humans naturally compare volume.  An 8-ounce glass may be only half the height of a half-gallon pitcher, but we can tell at a glance that the latter is not merely twice as large (what we would guess from the height).  And volume for a sphere is proportional to the diameter cubed, so Jupiter's volume is over 1000 times that of Earth.

By constructing a 3-D model with dough, that will be easy to see.

Note: the crossword puzzle relies on access to another handout that I am unable to put on the web.  You can get equivalent data on the physical properties of the planets from a web site like http://www.nineplanets.org/