Friction is unavoidable in our day-to-day lives. Man keeps trying so many techniques to reduce friction in any process, but he also realises that without friction none of his work would have been possible. Life would have been impossible without the aid of friction. Yet friction is termed as an evil. Without friction one can't walk, write, sit on a chair without slipping off or for that matter, even properly hold on to his or her morning cup of tea.
Friction is the retarding force coming into play when two bodies are in contact with each other.
Friction formula in general is given by
Ff is the magnitude of friction,
$\mu$ is the coefficient of friction and
is the magnitude of normal force.
The Normal force = Weight of the given body. Hence Normal force Fn
is given by
m is the mass of the body and
g is the gravity.
Friction formula is used to calculate the friction between the any two given bodies.