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- Pressure - by Rifki Irawan & Fiqri Hakim Definition of Pressure Liquid and Atmospheric Pressure Pressure Measurement

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Definition of Pressure Pressure is the force acting normally or perpendiculary per unit area Pressure = force area P (Pa) = F (N) A (m 2 ) SI unit for Pressure is Pascal (Pa) = 1 N m -2

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Weight = 100 N Area = 0.1 m 2 Pressure = 1000 Pa Weight = 100 N Area = 0.01 m 2 Pressure = 10,000 Pa “ same force, different area, different pressure “

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Example 1. The wind pressure on the wall is 100 Pa. If the wall has an area of 6 m 2, what is the force exert on it? To solve this problem, you need to rearrange the pressure equation: Force = pressure x area = 100 Pa x 6 m 2 = 600 N

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Example 2. A concrete block has a mass of 2,600 kg. If the block measures 0.5 m length by 1.0 m width and 2.0 m height, what is the maximum pressure of the concrete block that can exert when resting on the ground? (g = 10 m · s -2 ) F = mass x gravitasi = 2,600 kg x 10 m · s -2 = 26,000 N Area = 0.5 m x 1.0 m = 0.5 m 2 Pressure = force/area = 26,000 N / 0.5 m 2 = 52,000 Pa

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1.Pressure acts in all direction 2.Pressure increases with depth 3.Pressure depends on the density of the liquid 4.Pressure does not depend on the shape of the container Liquid and Atmospheric Pressure “A liquid exerts pressure because of its weight”

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Weight= mass x gravity Density = mass volume “pressure of the liquid depends on the density of the liquid itself” Volume liquid = base area x depth = A x h mass liquid = density x volume = x A x h Weight liquid = mass liquid x gravity = x A x h x g Weight liquid = Force of the liquid = A h g Pressure liquid = Force liquid Area container A h g A Pressure liquid = h g

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Example 1. If the density of water is 1.000 kg/m 3, what is the pressure due to the water at the bottom of a swimming pool 2 m deep? First, define the data which given Density= 1.000 kg/m 3 Height= 2 m Gravity= 10 N/kg Pressure = ρhg = 1,000 kg/m 3 x 2 m x 10 N/kg = 20,000 Pa

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Atmospheric pressure The athmosphere is a deep ocean of air which surround the earth. In some ways, it is like liquid: Its pressure acts in all directions. Its pressure becomes less as you rise up through it Unlike a liquid, air can be compressed.

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Atmospheric pressure The pressure that will support a column of mercury 760.0 mm hight is known as standard atmospheric pressure or 1 atmosphere (1 atm) 1 atm = 100.000 Pa In weather forecasting we often used milibar (mb) 1 mb = 100 Pa

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The instruments The mercury barometer Atmospheric press the mercury up the tube because the space at the top of the tube has no air in it. 760.0 mm Hg = 1 atm

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