There are situations where frictional force becomes a nuisance.
i. When the moving parts of a machinery rub against each other, they usually become hot due to friction. This may lead to wearing away of the parts.
ii. Friction due to air as liquid resistance reduces the speed of bodies in motion, e.g. an athlete running in the opposite direction of a strong wind has his speed reduced.
Reducing friction
The effect of friction can be reduced by
Lubrication: – The moving parts of the machinery are coated with lubricants (e.g. engine oil) to prevent them from rubbing against each other.
Frictional force contd.
R= mg
F= ma
F….R
F= MR
…m= F/R
If F= µR
=>F= µmg, ma= mg
i.e. ma=mg
But F= µR
But R=µg
F=mg
µ= F/mg
A body of mass 40kg is given an acceleration of 10m/s² on a horizontal ground for which the coefficient of friction is 0.5. Calculate the force required to accelerate the body, (take g= 10m/s², a= 10m/s²)
Given,
m= 40kg
f= ?
g= 10m/s²
Using fa – ff = ma
ff= mma
fa – ff= ma
fa= ma + ff
fa= ma + mmg
=40 × 10 + 0.5 × 40 × 10
=400 + 0.5 × 400
=400 + 200  