Friction is a force between two surfaces that are sliding, or trying to slide, across each other. For example, when you try to push a book along the floor, friction makes this difficult.

1.1 What is friction? Take this everyday example: when a coffee mug rests on a flat table, the kinetic frictional force is zero. There is no force trying to move the mug across the table, so there is ...

Perhaps few physical concepts have received less attention relative to their importance than friction. Learning the 'effective' notions of static and sliding friction, students of mechanics can ...