Measuring Pressure What does zero pressure look like

What does zero pressure look like? • There is no force applied to an

Two types of pressure measurements 1) Gauge Pressure • Assumes that atmospheric pressure is

Calculating Gauge Pressure • Gauge pressure = Absolute pressure – atmospheric pressure • pg

Two types of pressure measurements Absolute Pressure • Assumes that zero pressure is zero

Calculating Absolute Pressure • Absolute pressure = Gauge pressure + atmospheric pressure • pabs

Absolute Pressure is zero Gauge Pressure is zero

Ex 1 – Note: patm = 101 k. Pa You come out in the

Instruments • Barometer – Measures atmospheric pressure • Aneroid barometer – Does not use

Instruments • Altimeter – Measures altitude using the value of atmospheric pressure

Static Pressure Head • Height of a column of fluid that produces a specific

Calculating Pressure From Height of a Liquid pg = Dhg D – Density of

Ex 2: • If you dive to the bottom of a swimming pool that

Hydroelectric Dam • Greater the depth of a liquid, the greater the pressure •

‘Water seeks it’s own level’ • In an open container, all water will settle

Work • Pg 235 # 21, 23 • Pg 236 # 3, 7, 10,

Slides: 16

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Measuring Pressure

What does zero pressure look like? • There is no force applied to an area • If atmospheric pressure, there are no particles pushing on the surface • We call this a vacuum

Two types of pressure measurements 1) Gauge Pressure • Assumes that atmospheric pressure is zero pressure • Measures the difference between atmospheric pressure and an object with additional pressure

Calculating Gauge Pressure • Gauge pressure = Absolute pressure – atmospheric pressure • pg = pabs - patm

Two types of pressure measurements Absolute Pressure • Assumes that zero pressure is zero pressure • Measures the total pressure relative to a vacuum 2)

Calculating Absolute Pressure • Absolute pressure = Gauge pressure + atmospheric pressure • pabs = pg + patm

Absolute Pressure is zero Gauge Pressure is zero

Ex 1 – Note: patm = 101 k. Pa You come out in the morning and your car’s tire is flat. You read the side of the tire and it says “Maximum capacity 80 k. Pa” a) What is the initial gauge pressure in the flat tire? b) What will the gauge read after you fill the tire? c) What is the absolute pressure in the tire before and after the tire is filled?

Instruments • Barometer – Measures atmospheric pressure • Aneroid barometer – Does not use a liquid

Instruments • Altimeter – Measures altitude using the value of atmospheric pressure

Static Pressure Head • Height of a column of fluid that produces a specific pressure

Calculating Pressure From Height of a Liquid pg = Dhg D – Density of the liquid (kg/m 3) Dwater = 1000 kg/m 3 h – height of the liquid (m) g – Acceleration due to gravity (g = 9. 81 N/kg)

Ex 2: • If you dive to the bottom of a swimming pool that is 10 m deep a) What will be the gauge pressure be on your measuring instrument? b) What is the absolute pressure acting on you?

Hydroelectric Dam • Greater the depth of a liquid, the greater the pressure • Gravity pulls down the water, increasing the pressure on the bottom of the dam Thickest where pressure is greatest

‘Water seeks it’s own level’ • In an open container, all water will settle at the same level

Work • Pg 235 # 21, 23 • Pg 236 # 3, 7, 10, 11, 14 • Pg 244 # 5 -7, 9, 10