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What is pressure?
The elephant has a larger weight than the lady, but the contact area between its feet and the floor is far larger.
Why would a lady in high heels standing on your foot hurt more than an elephant standing on your foot?
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A force spread over a larger area produces a lower pressure.
High pressure and low pressure
Which type of footwear would be better for standing on a muddy field – the flat-soled shoes or high-heeled boots?
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The shoes have flat soles, so they spread the person’s weight over a large surface area.
These boots exert a low pressure on the ground.
High pressure and low pressure
In contrast, the soles of the high-heeled boots have a smaller surface area and so exert a higher pressure.
These shoes are likely to sink into soft ground.
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Pressure is measured in newtons per square metre (N/m2), which are also called pascals (Pa).
pressure =area
force
Pressure is the force per unit area and is calculated using this formula:
Calculating pressure
f
p a
This can also be represented in a formula triangle.
Pressure can also be measured in newtons per square centimetre (N/cm2).
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How much pressure is the woman exerting on the floor?
Pressure =
Pressure calculation
Weight of woman = 500 N
Area of contact with floor = 20 cm2
=
= 25 N/cm2
Area
Force
20
500
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A force spread over a large area produces low pressure. This is used in skis and snowboards.
The large surface area of the board means the snowboarder exerts very little pressure on the snow.
Using low pressure
This means he slides over the top of the snow and does not sink into it.
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A force concentrated on a small area produces high pressure. This is used in things like pins and sharp knives.
The narrow blade of a knife means that it exerts a high pressure, making it easier to cut fruit and vegetables.
The force applied to the tiny surface area of the end of a pin creates a high enough pressure to puncture even wood.
Using high pressure
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Investigating pressure
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Pressure – highest to lowest
