Chapter 11, Problem 29A

Is the net torque changed when a partner on a seesaw stands or hangs from her end instead of sitting? (Does the lever arm change?)

To determine

Whether the net torque changed when a partner on a seesaw stands or hangs from her end instead of sitting.

Answer to Problem 29A

No

Explanation of Solution

Introduction:

The torque acting about an axis of rotation due to the force $F$ is given by,

  $\begin{array}{c}\tau =F\times \left(r\right)\\ =F\text{r}\sin \theta \end{array}$

Where,

  $r=$ denotes the shortest distance of the point of application of force from the axis of rotation.

  $\theta =$ angle between the force and the distance

When the kids sat on the seesaw, their weight acts in downward direction. Hence, the angle between the distance and the force on the kids is $90°$ .

Now, when a partner on a seesaw stands or hangs from her end instead of sitting, even then the distance of point of application of force from the fulcrum will not change.

Conclusion:

Hence, the net torque does not change when a partner on a seesaw stands or hangs from her end instead of sitting.