Chapter 8, Problem 1CQ

To determine

Whether it is necessary that the object should be in static equilibrium when it is acted upon by two forces that are of equal magnitude and oppositely directed.

Answer to Problem 1CQ

It is not necessary that the object should be in static equilibrium when it is acted upon by two forces that are of equal magnitude and oppositely directed because the summation of the net torque should also be equal to zero.

Explanation of Solution

An object is said to be in static equilibrium when the net force and the net torque acting on the object is zero.

The condition for an object to be in static equilibrium can be summarized mathematically as,

First Condition.

    ${\displaystyle \sum F_{\text{x}}=0}$

Here, ${\displaystyle \sum F_{\text{x}}}$ is the summation of forces in the horizontal direction.

Second Condition.

    ${\displaystyle \sum F_{\text{y}}=0}$

Here, ${\displaystyle \sum F_{\text{y}}}$ is the summation of forces in the vertical direction.

Third Condition.

    ${\displaystyle \sum \tau =0}$

Here, ${\displaystyle \sum \tau }$ is the net torque in the body

Although the net force is balanced by equal and opposite forces, but the position of the applied force also plays a vital role. The position of the applied force should be such that net torque is cancelled by each other.

Therefore, it is not necessary that the object should be in static equilibrium when it is acted upon by two forces that are of equal magnitude and oppositely directed because the summation of the net torque should also be equal to zero.