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Causes of Friction
So what causes friction? In simple term, friction is caused by the "roughness" off the two surfaces that are touching each other. In general, the more rough the surface, the greater the force of friction.
Think about sandpaper rubbing wood and an ice skater skating on the ice. Both are examples of friction.
Of these two examples, which has more friction?
Even surfaces that feel smooth to us (like ice or the top of a desk) are still "rough" on a microscopic level, and this roughness leads to friction. This roughness is called microwelds. Microwelds are rough irregularities on the surface of objects that cause friction to occur. When objects come into contact with one another, their surface roughness causes friction.
Watch the following video to review what you have learned about friction: