We are studying wood.  We know that wood is a material and we observed wood's properties.  We looked at samples of pine, cedar, basswood, particle board and plywood.  The first three come from trees (pine from a pine tree, cedar from a cedar tree, basswood from a linden tree), but particle board is made from wood waste, saw dust, and glue and plywood is made from gluing layers of wood together.  We talked about what happens when wood gets wet- it either absorbs the water or the water beads up.  The pine absorbed the water, but the water beaded up on the particle board.  Next we talked about whether or not wood floats.  We saw that it floats even if we band a few pieces together and even if we leave it in the water overnight.  Today we talked about how we could get our wood samples to sink.  We used paper clips and elastics and found that 19 paper clips will sink. a pine sample.  We found that 17 or 18 paper clips will sink a particle board sample.   
We are really enjoying this unit!