rubber is a kind of material & wool is a kind of material & a rubber brush is rubbed on wool ->  a rubber rubbing on wool is an example of rubbing different materials together  a rubber rubbing on wool is an example of rubbing different materials together & rubbing different materials can cause electrical charge of the materials to be unbalanced ->  rubbing rubber on wool causes electrical charge of rubber and wool to be unbalanced  rubbing rubber on wool causes electrical charge of rubber and wool to be unbalanced & unbalanced electrical charge of material causes static electricity ->  rubbing rubber on wool causes static electricity on rubber and wool  rubbing rubber on wool causes static electricity on rubber and wool & static electricity can attract small, light-weighted object ->  rubbing rubber on wool can cause rubber to attract small, light-weighted object  rubbing rubber on wool can cause rubber to attract small, light-weighted object & small strips of paper are small and light-weighted & strips of paper are a kind of object -> rubbing rubber on wool can cause rubber to attract small strips of paper