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Form 4
Physics
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The study of matter
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Chapter 3:
Forces & Pressure
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Physics: Chapter 3
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Objectives:
(what you will learn)
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1)
understanding Pressure
2)
understanding the Principles
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Pressure
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Pressure = force per unit area
Pressure, P = Force, F , N m-2 or Pa (Pascal)
Area, A
If a fluid (liquid or gas) has a density ρ, its pressure
P, at a point due to the fluid of height h, is given by
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P = ρgh
where g = gravitational field strength
Therefore, for a given liquid, its pressure:
- increases with depth
- increases with density
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For a given point in the fluid, its pressure acts
equally in all directions.
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It does not depend on the shape of containers.
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Atmosphere
Atmosphere is the layer of thick air which
surrounds the Earth.
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The pressure exerted on the Earth’s surface by the
atmosphere is the atmospheric pressure, which
can be measured using Fortin barometer or
Aneroid barometer.
1 atmosphere
= 760 cm Hg
= 10.3 m water
= 101,300 Pa
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1 millibar = 100 Pa
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The Principles
Pascal’s Principle:
The pressure applied to an enclosed liquid is
transmitted equally to all parts of the liquid.
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Archimedes’ Principle:
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When an object is immersed in a fluid the buoyant
force on the object is equal in size to the weight of
fluid displaced by the object.
Bernoulli’s Principle:
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When the velocity of a fluid increases, the pressure
of the fluid decreases.
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Summary
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What you have learned:
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6
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1.
Understanding Pressure
2.
Understanding the Principles
Thank You