The Definition of Moments

Moments are a mathematical expression that involves the product of a physical quantity and its distance from a fixed reference point. The physical quantities are generally defined with reference to a fixed reference point. Consequently, a distance away from the reference point is a distance at which the moment is defined. This makes it easier to compare different physical quantities that have similar properties. In many cases, a distance between a point and its physical quantity is directly proportional to its moment.


Another definition of moments is a couple. A couple is a pair of forces that are equal in magnitude but opposite in direction. Unlike a single force, the couple does not cause a translation or rotation, but produces a pure moment. The moment created by the couple equals the force times the distance. An example of a couple is a wheel brace and two hands pushing in opposite directions. In equilibrium, the sum of moments about a point is zero.

A pure moment is defined as a moment that has no force, but only rotation. It is different from the force that is translated. A force must act in such a way that it causes the object to twist. In other words, a moment occurs when the force acting on the object does not pass through its centroid, or when there is no opposite force on the same line of action. This applies to the case of a nut as well.

A pure moment has no force. It is just rotation. The same principle applies to a force in the same way. The difference between a force and a moment is that a force that causes a rotation has the same reaction on any location. A total moment can be calculated anywhere on the body. The busiest joint is the most convenient. There is no point that cannot be described as the center of a moment. In other words, if a nut is rotating, it’s a pure moment.

A pure moment has no force, only rotation. A pure moment can be applied to any joint on the body. If the nut rotates, the force is a moment. Hence, a torque is a torque. The difference between a force and a torque is the degree to which a force causes a twist. The latter is the more convenient. Then, a torque is a moment. When a force is applied to a nut, the two forces are in motion.

A pure moment can be anywhere on the body. For example, if a wrench is applied to the nut, 100 pounds of force is applied at point C. In this case, the horizontal force is counteracted by a support stand. As a result, a pure moment is the same as a torque. However, the torque will be a direct result of a slack of a nut. It is, therefore, important to choose the right one for your application.