Page 193 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

Chapter 3 Scientific principles

Basic mechanics: moments of a force

(torque)

In physics, the moment of a force is the measure of the turning effect
(or torque) produced by a force acting on a body. It is equal to the applied force
and the perpendicular distance from its line of action to the pivot, about which
the body turns. The turning force around the pivot is called the moment. Its
unit of measurement is the newton.

IMPROVE YOUR MATHS
The moment of a force can be worked out using the formula:

Moment = force applied × perpendicular distance from the pivot
If the magnitude of the force is F and the perpendicular distance is d, then:

Moment = F × d

An example of this would be a spanner turning a bolt. It is
much easier to turn the bolt using a long spanner than it is
using a short spanner. This is because more torque (turning
force) can be applied at the bolt (pivot) for less effort. A The moment of a
force - the pivot
long spanner is an example of a force multiplier.
Centre of gravity Distance from

In physics, the centre of gravity of an object is the the pivot
imaginary point where all of the weight of the object is
concentrated. This concept is especially important when
designing large structures such as multi-storey buildings and
bridges, or making a prediction of the gravitational effect on Force applied
a moving object or body. Another term for it is the ‘centre
of mass’.
The centre of gravity will vary from object to object. In
symmetrically shaped objects, it will coincide with the Moment = Force applied × Distance from the pivot
geometric centre. = Newtons
p Figure 3.32 The moment of force
In irregularly (asymmetrically) shaped objects, the centre of
gravity may be some distance away from the centre of the
object; in hollow objects, such as a ball, it may be in free space, away from the
object’s physical form.

KEY POINT
For many solid objects, the location of the geometric centre follows the
object’s symmetry. For example, the geometric centre of a cube is the point
of intersection of the cube’s diagonals.

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