6. What exactly is Moment of a Force?

What is a moment of a Force?

The Moment of a force is a measure of its tendency to cause a body to rotate about a specific point or axis.

As stated by the definition of moment above we can deduce, as we move a body with mass away from the axis of rotation on the pivot, the moment (or torque) increases.

moment of Force
source

The picture above demonstrates moment in action. If we increase d (distance of Garfield from the pivot) the moment will increase. Adding to it, if we would increase the weight F the moment will also increase.

This leads us to our formula:

Moment=Fd

Where, F is the force

and d is the perpendicular distance from the axis at point O to the line of action of the force.

Moment being a vector quantity

  1. Magnitude: The units for Moment are Nm or lbft. Magnitude can be determined using the formula mentioned above.
  2. Direction: The direction of the moment can be determined using the moment axis (RHR). the moment Axis is perpendicular to the pane that contains the force F and its moment arm d.

Moment Axis —–> Out of the page —–> Anti-Clockwise

Moment Axis —–> Into the page ——> Clockwise

Resultant Moment

For 2D problems, the resultant moment about a point can be determined by finding the algebraic sum of the moment caused by all the forces in the system.

Also Read: Couple Moment part 2