In this entry:

1. What is a moment of force
2. Formula for moment of force
3. Torque unit
4. Marking the moment
5. How to calculate the moment of force with respect to a point
6. When the moment is zero

The moment of force is the product of the value of the force and the distance between the point of application of the force and the point at which we calculate the moment. Commonly referred to as: "force times arm."

Formula for moment of force

where:

F - load value in [N]

r - distance between the point of application F and the point at which we calculate the moment in [m].

Torque unit

The SI unit of torque is [Nm] - Newton times a meter

Marking the moment

Moment sign : - plus (+) - rotation of the force around a point O Counterclockwise, - minus (-) - rotation of the force around a point O Clockwise.

A more "scientific" definition of the moment of force is to represent it as a vector product. You can find such a definition in Wikipedia:

Moment of force relative to the point O - the vector product of the guiding radius r, with the beginning at the point O and the end at the point of force application, and the force F.

We will determine the direction and return of this vector using the "right hand" rule. Take your right hand, bent fingers aligned according to the direction of the load "F", the straightened thumb will show you the direction and return of the moment vector.

How do you calculate the moment of force?

To calculate the moment, we need to think about three things:

1. What kind of force do we want to include?
2. Relative to which point do we count the moment?
3. What is the arm on which this force acts?

Well, that's what we need the value of the force and multiply it by the arm. Arm that is, the shortest distance connecting the point of application F and the point at which we want to calculate the moment. Here are some examples.

The first example is easy for a warm-up. We have a force and we can determine the segment connecting this force to the point "O". The segment is at 90 degrees to the direction of the force. The result Mo= 40 [Nm]. Positive sign because the force rotates around the point "O" counterclockwise.

The second example a little more complex. We have a force for which it is not so easy to determine the distance to the point "O". As you will see in Fig.2 on the right we decompose the force F into two components: horizontal and vertical. And now we already easily find the segments connecting the point with the direction of these components, I called them rx=3m and ry=5m.

Below is the calculation of momentum relative to point "O":

When the moment is zero

The moment will be zero if one of the components of the equation is zero:

• Force F=0
• arm r=0 - that is, the force passes through the point relative to which we calculate the moment of force.

That's about it, regards 😊