F

93 Pages·2013·4.83 MB·English

5. (II) A bottle has a mass of 35.00 g when empty
and 98.44 g when filled with water. When filled
with another fluid, the mass is 88.78 g. What is
the specific gravity of this other fluid?
5.  Take the ratio of the density of the fluid to that
of water, noting that the same volume is used
for both liquids (so V cancels).
SG

1
ΔP = ρgh
= (1.05 x 103 kg/m3)(9.8m/s2)(1.60m)
1mmHg
= 1.646 x 104 N/m2
×
2
133N /m
= 124 mmHg
€
2
9.  (I) (a) Calculate the total force of the
atmosphere acting on the top of a table that
measures
(b) What is the total force acting upward on the
underside of the table?
9. (a) The total force of the atmosphere on
the table will be the air pressure times the area
of the table.

(b) Since the atmospheric pressure is the same on the underside of the
table (the height difference is minimal), the upward force of air pressure is
the same as the downward force of air on the top of the table,
3
10.(II) In a movie, Tarzan evades his captors by
hiding underwater for many minutes while
breathing through a long, thin reed. Assuming
the maximum pressure difference his lungs can
manage and still breathe is 85 mmHg, calculate
the deepest he could have been.
10.The pressure difference on the lungs is the
pressure change from the depth of water
4
Atmospheric Pressure
•  Earth’s atmosphere: A fluid.
•  ⇒ Change in pressure: ΔP = ρgΔh
•  At sea level: P ≡ 1.013 × 105 N/m2
0
= 101.3 kPa 1 atm
≡
The cause of (air) pressure at any height
in atmosphere is:
weight of air above that height!
Measurement of Pressure; Gauges and the
Barometer
There are a number of different types of
pressure gauges. This one is an open-
tube manometer. The pressure in the
open end is atmospheric pressure; the
pressure being measured will cause
the fluid to rise until
the pressures on both
sides at the same
height are equal.
6
Pressure beneath surface of liquid open to the atmosphere
Gauge Pressure
Initial Pressure (atmospheric pressure)
ABSOLUTE PRESSURE
Gauge Pressure = The amount by which P
exceeds atmospheric pressure P
o
7
Gauge Pressure
•  Pressure gauges (like tire gauges, etc.)
measure difference between
atmospheric pressure P & internal
0
pressure (of tire, for example).
•  Gauge pressure: P = P – P

G 0
Measurement of Pressure; Gauges and the
Barometer
Here are two more devices for
measuring pressure: the tire
pressure gauge and the
aneroid gauge.
9
Measurement of Pressure; Gauges and the Barometer
This is a mercury barometer,
developed by Torricelli to measure
atmospheric pressure. The height of
the column of mercury is such that
the pressure in the tube at the
surface level is 1 atm.
Therefore, pressure is often quoted
in millimeters (or inches) of
mercury.
10