Question

The amount of friction divided by the weight of an object forms a unitless number called the _____ of friction.

Answer 1

ANS: The correct answer to the question is coefficient of friction.

EXPLANATION:

Let us consider a body resting on a table. The weight of the body is acting in vertical downward direction. The table also exerts an equal amount of force perpendicular to the surface of the body which is called normal reaction.

Here, normal reaction [N] = Weight [W]

Let an external force is applied on the body which will cause motion on the body. As the body is resting on the floor, friction will come into existence which will oppose the relative motion between table and body.

Let F is the force of friction.

The force of friction is directly proportional to the normal reaction. Mathematically we may write F ∝ N

                                              $F=\mu N$

Here, $\mu$ is a proportionality constant called the coefficient of friction.

$The\ coefficient\ of\ friction\ \mu=\frac{F}{N}$

                                           ⇒ $\mu\ =\ \frac{F}{W}$  [∵N= W]

From above, it is obvious that coefficient of friction is a unitless quantity.

Hence, the amount of friction divided by the weight of an object forms  a unitless number called the coefficient of friction.