When Does Force Come Into Play?

What is the requirement for a force to come into play?

A chapati maker is a machine which converts balls of dough into chapati’s. What effect of force comes into play in this process?

Moment of inertia comes into play

Whenever the surfaces in contact tend to move or move with respect to each other, the force of friction comes into play

Will force of friction come into play when a rain drop rolls down a glass window pane?

Which type of friction comes into play when a book kept on cylindrical pencils is moved by pushing ?

What kind of friction come into play : when a block of wood kept on table just tends to move (or slip) ?