Moments: Definition, Formula and Calculation

What is Moments?

By definition Moments, also known as torque, is the turning effect of a force. Moments can either be in a clockwise or anti-clockwise direction. The unit of moments is the Newton Meter (Nm).

Formula for Moments of a force:

      Moments (torque) = Force × Perpendicular distance from the pivot

How to calculate Moments?

Example 1
Find the total moments of the system below:

Diagram Showing Moments

Step 1

Identify which force in the system is moving in the clockwise direction and which is moving in an anticlockwise direction. The 50N force is the one moving in the clockwise direction (the same direction a clock’s pointer would move) while the 80N is moving in the opposite direction (anti-clockwise direction).

Showing Clockwise and Anti-clockwise Moments

Step 2

Use the formula given above to calculate the clockwise and anti-clockwise moments separately.

          Moments = Force × Perpendicular distance

          Clockwise Moments = Force × Perpendicular Distance
                                          = 50N × 6m
                                          = 300Nm

          Anti-Clockwise Moments = Force × Perpendicular Distance
                                                  = 80N × 4m
                                                  = 320Nm

Step 3

Now that you have calculated both clockwise and anti-clockwise moments you can now find the total moments of the system. This is found by subtracting the smaller moments from the larger, in this case the smaller of the two is the clockwise while the larger is the anti-clockwise.

         Total Moments = 320Nm – 300Nm
                                 = 20Nm in the anti-clockwise direction

 Note: Anti-clockwise direction is written at the end because it is larger.