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This problem is great for stimulating discussion at the start of a mechanics course.
This problem is easy to introduce to a class according to the order suggested in the problem, but you might like to keep the existence of the Gombocs as a surprise. As you lead the exploration, be on the lookout for opportunities to introduce and reinforce key concepts and vocabulary as students strive to articulate their thoughts. Examples might include: uniform density; equilibrium; perturbation; stability; symmetry; mathematical model; configuration; static; centre of mass; magnitude; vectors and forces. Preparing the ground in this way before rushing into content is time well spent!
Throughout, demand clarity of thought and speech.
Can you arrange a set of charged particles so that none of them start to move when released from rest?