Page 186 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

The City & Guilds Textbook: Plumbing Book 1

Force

Force is an influence on an object at rest that, acting alone, will cause the motion
of the object to change. If the object at rest is subjected to a force, it will start
to move. For example, consider water in a pipe connected to a cistern at one end
and a tap at the other. When the tap is closed, the water is not moving and so
is said to be at rest. When the tap is opened, the force of gravity will move the
water out of the tap, causing water to flow. It is measured in newtons (N).

IMPROVE YOUR MATHS
The unit of the force of gravity is the newton. It is the force required to
accelerate a mass of 1 kg at 1 metre per second, every second. On Earth, that
force of acceleration (known as gravitational pull) is 9.81 metres per second per
second, or 9.81 m/s . Therefore, if we multiply the mass of an object (in kg) by
2
2
9.81, the result is measured in newtons (kgm/s ).

ACTIVITY
Calculating force
When the tap is When the tap is opened,
Consider the cistern in closed, the body of the force of gravity
Figure 3.19. If it contained water is at rest pushes the water down
a mass of water equal to the pipe and out of the
tap causing a flow of
40 kg, then by multiplying water
the mass by the force of
gravity, the force of the
cistern acting downwards
can be calculated:

40 × 9.81 = 392.4 N
If a cistern in a roof space
contains a volume of
100 litres of water and
1 litre = 1 kg, what is
the force acting on the
platform it is standing on?
p Figure 3.19 The force of gravity on a cold water system

Pressure
In physics, pressure is defined as force per unit area. For an object sitting on a
surface, the force pressing on the surface is the weight of the object measured
2
in newtons per square metre (N/m ). However, in different orientations it
might have a different area in contact with the surface and will therefore exert

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