PHYSICS 5B Lecture Notes - Lecture 9: Hydrostatics, Atmospheric Pressure
Fluid Mechanics
-Fluids -liquids and gases
↳liquids =acollection of randomly arranged atoms and molecules bond together by internal cohesive forcee
*difficult To compress (like solid
,
unlike gases)
↳gas you can have avolume that you can easily compress
↳liquid don't maintain it 's shape under external force (like gases ,unlike solids )
-Density =mass /volume =P= F(kg/m3)
e± density for air =1.2 kglm '(gas )
density for water =1.0×103 ky|m3 (liquid
)
density for copper =8.9×103 kg /m3 (solid )
-General definition of pressure :P= ¥ascalar quantity
qFt
y11/4/11
'normal force
Asurface area
for an arbitrary shape P.
'dh¥ ,unit s,F=Pa
Earth atmosphere at sea level :Pavg .
.Iatm =1.013 x105 (Pa)=14.7 (Psi t
16hm)=1.013 (bar )
-Hydrostatics :Empirical facts :
(i)the pressure at some point In aliquid Is The same in all directions
(2) pressure is height dependent p(h=o )=Po =latm
e± .Pis lower In the high mountain ^
-Airplane cabin has to be pressuring n
"#•¥a¥p#%
-Swimming in deep water ✓
PC h)
why ?Due to the weight ot the fluids
want Pas afunction of y
It
!
.t¥←P -volume of The sample .
.dv= Ady
y¥ah¥dY mass of liquid =dm =
Pdf rho
=P Ady
gravitational force =dw =(dm ).
g
=Pg Ady
Newton 's first law
ttz
f. .tz -dw .-0
dwt TF
,PA
-(PTDPVA
-Pg
#dy=0
If
-DP -Pgdy =0
DI =-Pg
dy
ftp.fpgdvfp.kdp.ly
,
"
-pgdy ⇒Pz -P
,
=-pgyh?2= .pg( yz
.y,)
Pz .P,
.
' -
Pg (yz -YD
