1. Measuring Pressure

2. 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

3. 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

4. Calculating Gauge Pressure Gauge pressure = Absolute pressure – atmospheric pressure p g = p abs - p atm

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

6. Calculating Absolute Pressure Absolute pressure = Gauge pressure + atmospheric pressure p abs = p g + p atm

7. Absolute Pressure is zero Gauge Pressure is zero

8. Ex 1 – Note: p atm = 101kPa 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 80kPa” 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?

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

10. Instruments Altimeter – Measures altitude using the value of atmospheric pressure

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

12. Calculating Pressure From Height of a Liquid p g = Dhg D – Density of the liquid (kg/m 3 ) Dwater = 1000kg/m 3 h – height of the liquid (m) g – Acceleration due to gravity (g = 9.81N/kg)

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

14. 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

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

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