Friction - July Dec Revision

1. Normal force = N_f = Mg
Where
M = mass of the object
g = acceleration due to gravity



2. f_k = µ_k N_f
where

f_k = magnitude of kinetic friction
µ_k = coefficient of kinetic friction

3. f_max = µ_s N_f

where

f_max = maximum static friction
µ_s = coefficient of static friction

The actual static friction can be less than maximum static friction if the force applied is less than f_max .

4. On an adjustable inclined plane, a block is kept and the angle is gradually increased so that the block begins to move.

Then f_max = mg sin θ
N_f = mg cos θ

There coefficient of static friction µ_s

µ_s = f_max / N_f
= tan θ = h/d

where θ = angle of incline when the block starts moving
m = mass of the block placed on incline
h = height of the incline
d= length of the incline

5. T find kinetic friction the angle of the incline is slightly reduced and the block is made to move with uniform velocity

In this case
µ_k = coefficient of kinetic friction = tan θ’ = h’/d’
(h is going to decrease and d is going to increase)


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