Question

What is the difference between static and kinetic friction. Define both, write their SI unit and dimension. Write down the mathematical statement (formula) that allows us to calculate the force of friction. Explain each term with its unit. Let’s say you’re dragging a 50 kg rubber box on wetconcrete. How do you calculate the force of friction on this box?

Answer 1

the major difference between these two friciton force is that, the static fricitonal force on the object which is static or stationary i. e. the fricitonal force which acts on object when it is in rest position is called static friciton.

for example : we can't move a stationary truck by appmying force by hand, this is due to static fricitonal force.

magnitude,

Fs = (us) Mg

where, us = coefficient of static friction

M = mass of the object

g = acceleration due to gravity

unit = N

dimension = MLT^-2

Direction,

it always directed in the opposite direction of force applied.

value of us is depend on the two surface ( object and floor).

==========

but the fricitonal force acts on the object when it is in motion then the force of friciton is called kinetic friction force.

for example

if we roll a football on ground, after travelling some distance it will stop its motion. so the frictional force acting onthe ball throughout its moving distance is known as kinetic friciton.

Fk = uk Mg

uk = coefficient of kinetic friction

Direction,

it always direct opposite to the direction of motion.

unit = since it is also a force so

unit = Newton (N)

dimension = MLT^-2

==========

another difference between these two is, kinetic friciton is always constant but static friciton ranges from 0 toits limiting value of friciton.

========

Comment in case any doubt, will reply for sure.. Goodluck