Friction is created between surfaces which rub together. Smooth surfaces produce less friction.
Snowboards and skies are designed with very smooth surfaces underneath them, to allow them to travel as quickly as possible over the snow and ice.
Rough surfaces produce large forces of friction.
Although not solid materials, air and water create rubbing surfaces when objects travel through them. More friction is created when there is a large surface area 'rubbing' against the air or water. We call this friction resistance.
Fish have a smooth shape and surface to reduce the amount of water resistance as they swim, allowing them to swim quickly.
Rockets also have a smooth shape and surface to reduce air resistance.
Use this worksheet to see if there are any rough edges to knock off friction and resistance.