http://serc.carleton.edu/spaceboston/2011activities/57620.html#discussion http://serc.carleton.edu/spaceboston/2011activities/57620.html#post18302 In the summary, perhaps you could talk a little more about what the students should know about "states and properties of matter" before they begin here.
I worry that the students will not be able to do this in 45 minutes. Do you think it'll fit?
Under Background: Your description is fine, except the lighter "floating" materials are the planet's mantle, not necessarily the crust. The crust of a planet may or may not form during a magma ocean solidification.
I am not sure what the purpose of the three materials are. Ball bearings, as long as they are predominantly iron, represent the core. What do the two others represent? What are fishtank pebbles made of? You might want a basalt (lava), kind of representative of the mantle (well, it's a partial melt of the mantle), and a quartz pebble, kind of representative of the crust (because it is higher silica and should be less dense than basalt), but these are inexact and quite possibly confusing. So how about one silicate rock, and then the iron?
Thanks for writing an interesting activity! I hope you will do edits and post it publicly, and that you will continue to edit it over the year when you use it in your classroom.
]]> Lindy Elkins-Tanton 1312498500 http://serc.carleton.edu/spaceboston/2011activities/57620.html#post18302 http://serc.carleton.edu/spaceboston/2011activities/57620.html#post18332 I'll be interested to learn how kids go about the first part of the activity, and whether the groups come up with different ways of determining density. It seems that it will work well as an assessment opportunity for you, and that it could easily take the 45 minutes.
Since you want to link the activity to planetary differentiation, you could think about it using it later, after you have talked more about that process. You could ask kids to figure out which material would be likely to be found in the mantle, and which in the core.....
As for part 2, I'm remembering some variations on what you planned that were proposed in class. One (from Lindy?) was that kids could calculate the density of a planet that was half one material and half another. There were some other ideas, I think, aimed at giving kids enough information that they could carry out a calculation that would make sense. Maybe folks can add those to the discussion.....
Keep us posted as you move ahead with this!
Ellen]]> Ellen Doris 1313439240 http://serc.carleton.edu/spaceboston/2011activities/57620.html#post18332