1. Measuring Pressure

2. Atmospheric Pressure Recall: Caused by the weight of the air molecules above us. Typically 101.3 kPa or 101 300 Pa Measured using a barometerbarometer An altimeter is a device in an aircraft that measures the altitude of a plane using a barometer and relating that to 101.3 kPa.

3. Gauge Pressure Most pressure readings of gases and liquids are called gauge pressure. They do not measure the absolute (total) pressure which includes atmospheric pressure. Relationship: Gauge pressure = Absolute Pressure – Atmospheric Pressure Using symbols:

4. Manometer Manometer: A device that measures gauge pressure. Uses the weight of a fluid and the height difference. As pressure increases Height difference increases Water weight increases h p atm p system U-tube manometer

5. Pressure in a Manometer Using our pressure equation we can derive the gauge pressure in a manometer: *Weight of the water is mass x gravity *Mass = density x volume * Since V = Ah; h = V/A Gauge pressure formula Where: D= density (kg /m 3 ) h = height of fluid (m)

6. Example #1 A pump is connected to one tube of manometer containing water (D = 1000 kg / m 3 ). Pressure is increased until the static pressure head (h) is 15 cm. What is the gauge pressure?

7. Example #2 Calculate the absolute pressure in the water behind a dam with a static pressure head of 18.0 m. The atmospheric pressure at the dam is 1.00 x 10 5 Pa

8. Blood Pressure Measured using a sphygomanometer. Two numbers Systolic: Maximum blood pressure Normal value = 16 kPa Diastolic: Minimum blood pressure Normal value = 11 kPa Given to you by your doctor as “16 over 11”.