Planets and their orbits

Today I brought the coin funnel to Primaria and we learned how orbits work.  One four-year-old came up with Kepler's 3rd Law all by himself!  With 6-8 kids in each group I organized it by having each child raise a quiet hand, tell me something they know about planets or the Sun, and then I gave that child a marble to roll in the well.  That gave me a chance to comment on what we could learn from each marble.  Depending on how it was thrown, the lesson could have been about escape velocity, about planets not falling straight into the Sun, about all the planets going around in the same direction, etc. Most of the time we pretended the Sun was at the center but if you want to make it more exciting you can pretend it's a black hole. 

Then  we shifted gears and built a scale model of the solar system: I showed a basketball representing the Sun, and I laid out various objects (a tomato, a grape, a small candy, etc) for them to choose which one they thought was the right size to represent Jupiter, the Earth, etc.   The correct answers are truly amazing: learn more at this well-written site. We didn't have time to go outside and put the correct distances between the planets, but I did describe the highlights of that aspect: Earth would be roughly in the office if we were with the Sun in the P1 room.

Aside on teaching and learning: one aspect of orbits is that all objects in a given orbit go at the same speed, regardless of their mass (technically, as long as the mass is much smaller than the mass of the thing being orbited).  To reinforce that, I dropped two marbles of very different mass and asked which one would hit the ground first.  Of course, many had the misconception that the heavy one would hit first.  I remark on it now because I had done the same demo with the same kids eight weeks ago in a slightly different context, so it's clear that they forgot.  These misconceptions are persistent!