Disadvantages of friction
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
Answer=600N
Streamlining: – The shapes of ships, boats, aeroplanes and submarines are modelled after that of fishes with pointed or blunt and slightly curved sides. This type of shape ensures that only a small surface area is in head-on contact with the fluid during motion. This enables the vessels move through fluid with minimum friction.
Again, the birds of the air/sky are naturally shaped to move without friction in the air. So, objects that move in air are shaped like the birds e.g. aeroplanes.
Scalars and vectors
Scalar quantity: – This is a quantity with only size or magnitude, e.g. 10m length, 20kg mass etc.
Vector quantity: – This has both size and magnitude, e.g. a car moving from Owerri to Port-Harcourt has a particular direction to follow i.e. 100m east, displacement or 100m/s due east, velocity. Other examples include force, weight, momentum, acceleration etc.
The following table outlines some examples of scalars and vectors.
