The force which opposes the relative motion of a body over another is called

The force of friction is always _____ to the two surfaces.

The maximum value of the static friction is called _____ friction.

When one body moves over the other, the force of friction acting between the two surfaces is called _____ friction.

The force of friction which comes into play between two surfaces when one tends to slide over the other is called ____ friction.

Rolling friction (fr) is force of friction which comes into play between two surfaces, while one is rolling over other is called ___ friction.

Which is a suitable method to decrease friction? 

Streamlining the bodies to ____ friction.

$f\propto R\Rightarrow f=\mu R\mathrm{.}f\; \backslash propto\; R\; \backslash Rightarrow\; f=\; \backslash mu\; R.$ Where µ is 

Which is a suitable method to increase friction?