The moment of a force (M) is the force multiplied by the perpendicular distance to the fulcrum.1 A fulcrum is a fixed point about which a rigid body (called a level) is free to rotate.
Moment is the turning effect of a force.A force can have a clockwise turning moment or an anticlockwise turning moment. This means that the direction must be taken into consideration when dealing with moments.
It is a vector quantity with an SI unit of newton metre (N m). MOMENT OF FORCE
M Fd M moment of the force, F force, d the perpendicular distance from force to the fulcrum
In order to determine the magnitude of the moment of a force, or if the force is providing a clockwise or anticlockwise moment, we must first decide on the axis. Moment of force can only be determined with reference to an axis.
SAMPLE PROBLEM 4A Calculate the turning effect of a 7 N force applied at right angles to a door at a distance of 80 cm from the hinge.
SAMPLE ANSWER 4A
Using the formula for moment of force, making sure all values are in their standard unit: M Fd (7)(0.8) 5.6 The turning effect of the force is 5.6 N m.
1A more accurate definition would be:‘The moment of a force about an axis is the force multiplied by the perpendicular distance from the axis to the line of action of the force.’ At Leaving Cert. level we only consider parallel forces; it is therefore acceptable to use an abbreviated definition of moment of force.
