Smooth surfaces have less friction than rough surfaces .Therefore,we can reduce friction by either making a surface smooth or
adding a layer of liquid to it.For this purpose,many different methods are used.Some are:
1-Polishing:The floor of a newly-built building is always rough.The floor is polished in order to make it smooth.Thus,polishing is
a common way to reduce friction of the floor.
2-Using wheels and ball bearings:It is difficult to slide a load over a ramp without using a trolley.This is because the trolley has
wheels,which convert sliding movement into rolling movement.The friction of a rolling object is always less than the friction of a
sliding object.Therefore,wheels and ball bearings are used in machines to reduce friction.
3-Adding lubricants:When a door-lock is jammed,we need to put some oil in it..A lock gets jammed due to an increase in
friction between its parts.Oil and grease are common forms of lubricants that are used to reduce friction between the moving
parts of machine.