Question

Choose the incorrect statement from statements given below:

• A. Friction is an electromagnetic force.
• B. Value of static friction is always greater than kinetic friction.
• C. Coefficient of static friction is greater than coefficient of kinetic friction.
• D. None of these

Answer 1

The correct option is B Value of static friction is always greater than kinetic friction.

Friction is a parallel component of contact force that results due to the forces acting between the charged components (i.e electron, proton) of atoms of the two bodies/surfaces in contact.
$\therefore$ Friction is an electromagnetic force.

$\Rightarrow$The relation between coefficient of static and kinetic friction is ${\mu }_s\ge {\mu }_k$
But value of static friction is not always greater than kinetic friction. Static friction $f_s$ adjusts its value in the range $(0\le f_s\le {\mu }_{s}N)$ to prevent the relative motion between surfaces in contact.
$\Rightarrow$ Once slipping happens then kinetic friction $(f_k={\mu }_{k}N)$ acts on body, which is constant.
$\therefore$ Option $\left(b\right)$ is the incorrect option.