Weegy: Friction can be increased by using a rougher, or coarser, material. Sand paper is one example.
Friction can be reduced by using a smoother material, this can be silk, or very very finely milled metal. [ Additionally, lubricants like oil can be used, the oil gets between where two materials make contact and effectively fills in the gaps to make rough surfaces become smoother, and allow them to slide past each other more easily. ] (More)