فشار(Pressure)
فشار چیست؟
معادلات فشار
P = F/A
P = نیوتن (Kg x m/s/s)
عرض x طول
Pascals or N/m²
فشار خیلی پایین
فشارهای بالاتر
کل سیستم فشار پایینی دارد اما در دهانه گرداب فشار بسیار پایین است و به این دلیل جریان گردابی شدیدی ایجاد می شود.
فشار ستونی از مایع
با افزایش ارتفاع آب در ستون فشار آن نیز افزایش
می یابد.
The first device for measuring atmospheric
pressure was developed by Evangelista Torricelli
during the 17th century.
The device was called a “barometer”
Baro = weight
Meter = measure
Evangelista Torricelli, circa 1644
Measuring Pressure
“We live submerged at the
bottom of an ocean of air.”
Barometer
Vacuum
Height of column
29.92 in. (76 cm)
Air pressure
Air pressure
Mercury
Barometer
Vacuum
Height of column
29.92 in. (76 cm)
Air pressure
Air pressure
Mercury
Barometer
Mercury filled
760 mm = 1 atm
Water filled
10400 mm = 1 atm
The barometer measures
air pressure
Water column
(34.0 ft. high
or 10.4 m)
Atmospheric
pressure
Mercury column
(30.0 in. high
or 76 cm)
تغییرات نقطه جوش با ارتفاع
Water exerts a vapor pressure of 101.3 kPa at
a temperature of 100 oC. This is defined as its
normal boiling point:
در نقطه جوش فشار بخار مایع با فشار اتمسفری برابر می شود.
x kPa = 253 mm Hg (101.3 kPa) = 33.7 kPa
(760 mm Hg)
Manometer
lower
pressure
higher
pressure
P1
Pa
height
750 mm Hg
130 mm
higher
pressure
880 mm Hg
Pa =
h =
+
–
lower
pressure
620 mm Hg
Manometer
Pb
Pa
750 mm Hg
Pa =
lower
pressure
Manometer
Pa
height
750 mm Hg
130 mm
lower
pressure
620 mm Hg
Pa =
h =
–
880 mm Hg
higher
pressure
higher
pressure
Manometer
Pa
height
750 mm Hg
130 mm
Pa =
h =
+
Manometer
Pb
Pa
750 mm Hg
Pa =
lower
pressure
Manometer
Pa
height
750 mm Hg
130 mm
lower
pressure
620 mm Hg
Pa =
h =
–
880 mm Hg
higher
pressure
higher
pressure
Manometer
Pa
height
750 mm Hg
130 mm
Pa =
h =
+
جادوییU-tube
Evaporates Easily
VOLATILE
HIGH Vapor Pressure
Evaporates Slowly
LOW Vapor Pressure
AIR
PRESSURE
15psi
AIR
PRESSURE
15psi
AIR
PRESSURE
15psi
4 psi
2
الکل آب
Barometer
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 451
(a)
(b)
(c)
تبخیر
تبخیر
H2O(g)
molecules
(water vapor)
H2O(l)
molecules
تبخیر
H2O(g)
molecules
(water vapor)
H2O(l)
molecules
روش اندازه گیری فشار بخار
1 atm = 760 mm Hg
760 mm + 120 mm = 880 mm Hg
Animation by Raymond Chang
All rights reserved
dropper
containing
a liquid
atm. pressure
atmospheric
pressure
mercury
vapor from
the liquid
120 mm