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8.1 Pressure of solids
Imagine you are near In the previous units we learnt how to draw force arrows and read about
a frozen pond or river different types of forces: weight (the force of gravity), friction and its
and you suddenly different types and the Normal force (the force a surface exerts on an
hear a call for help. object on top of it). We learnt that when we have more than one force,
textbooks nis edu kz
we add or subtract them to arrive at the resultant force.
Somebody has fallen
through the ice. What The result of force action on a support depends on the magnitude and
are you going to do? direction of that force and also the point of application of the force.
Importantly, the result of force action also depends on the surface area
The first rule is that
on which it is acting.
you should never run
or walk across ice, but The ratio of how much force is applied in each point of application
(i.e. the area) is known as pressure. Pressure is a physical quantity
rather crawl. Why do
describing how the force of one object acts on another object
you have to crawl?
or surface.
force F
pressure = or p =
area A
p (lower case) = pressure
F = force acting on surface perpendicularly (this is measured in Newtons)
2
A = area (or object’s area of support) (this is measured in m )
Pressure units are measured in SI:
N
[p] = 1 = 1 Pa (Pascal)
m 2
1 kPa = 1000 Pa
REMEMBER! Pressure is a physical quantity that is equal to the ratio of
force perpendicular to the surface and the area of application.
THINK ABOUT IT! Why is a person able to lie down on a bed of nails
without getting hurt, when they would be injured if they lay down on a
single nail?
Ice rescue training
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