Question

what forces moved the pieces of wood? how did the forces relate to the direction of the oil flow in the bin

Answer 1

The forces that moved the pieces of wood were likely the buoyancy of the oil and the force of gravity. The buoyancy of the oil would have caused the pieces of wood to float and move in the direction of the oil flow. The force of gravity would have caused the pieces of wood to move downwards in the direction of the oil flow.