What is the formula of friction?

Friction is a force that opposes the motion of an object. There are two types of frictions,

STATIC FRICTION

KINETIC FRICTION

static friction , F s max ​ = μ s ​ F n ​ where μ s = coefficient of static friction and Fn is the normal force

kinetic friction, F k ​ = μ k ​ F n ​ where,

μ k= coesfficient of kinetic friction

In asking this question, you my not have realized that most work that occurs on the horizontal plane is done by friction, and against friction.

As was mentioned, work = force x distance.

With friction, force = uN where N is the force between two surfaces, and u is the co-efficient of sliding friction ( static friction does no work whatsoever, since there is no distance involved ).

So work = u x N x d

The co-efficient of friction between two surfaces, multiplied by the force between two surfaces multiplied by the distance traveled of one surface relative to the other.

Finally, work usually is done by friction to overcome friction, so be careful of your context. You can probably quantify this in your answer.

Sorry I think there's some printing mistakes in my previous answer

Friction is a force that opposes the motion of an object. There are two types of frictions,

STATIC FRICTION

KINETIC FRICTION

static friction Fs = UsFn where (Us (mu) = Coefficient of static friction and Fn = Normal force)

kinetic friction Fk = UkFn where (Uk = Coefficient of kinetic friction