Pressure, pressure calculations

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IGCSE Physics
Pressure

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Pressure
Contents
Pressure in liquids
Pressure

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Pressure is exerted whenever a force is applied over an area.
If the same force is applied in each picture, which arm exerts
the highest pressure on the board?
1. 2.
What is pressure?

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The arm applies a force
to the board via a fingertip.
The force acts over a
small area and so
produces a high pressure.
1.
High and low pressure
The same force is now acting
over a larger area – the palm
has a greater surface area
than the fingertip.
A lower pressure is produced.
2.

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Pressure is measured in:
Newtons per square metre (N/m2
), which are also called
pascals (Pa).
Pressure can also be measured in:
Newtons per square millimetre (N/mm2
);
Newtons per square centimetre (N/cm2
).
pressure =
area
force
P x A
F
Pressure is the force per unit area
and is calculated using this formula:
Calculating pressure

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The same force spread over a larger area means a lower
pressure.
Which type of pressure?
Which type of shoes would be best for walking over a muddy
field – flat soles or heels?

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The boots have flat soles
and spread the person’s
weight over a large surface
area.
These boots exert a low
pressure on the ground.
Which type of pressure?
In contrast, the heeled
shoes have a smaller
surface area and so
exert a higher pressure.
These shoes are likely
to sink into soft ground.

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A force spread over a large area means low pressure,
e.g. skis and snowboards.
The large surface area
of the board means the
skier exerts very little
pressure on the snow.
This means he slides
over the top of the snow
and does not sink into it.
Using low pressure

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A force concentrated on a small area means high pressure,
e.g. high heeled shoes, needles, ice skates, sharp knives.
The narrow blade of a knife
means that it exerts a high
pressure and makes it easier
to cut fruit and vegetables.
The high pressure of the
blade of an ice-skate melts
the ice and helps the skater
slide across the surface.
Using high pressure

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Pressure
Contents
Pressure in liquids
Pressure
Summary activities

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Pressure in a liquid:
 acts in all directions;
 increases with depth.
Pressure in a liquid
A liquid can be used to transmit
pressure from one place to
another.

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high pressure
low pressure
The relationship between pressure and depth is shown
by a water bottle with holes along its length.
Pressure in a liquid