PowerPoint Presentation in Physics (Fluids)

1. PHYSICS 203L1 LECTURE
First Semester 2012-2013
Group III - CE31FA1
Technological Institute of the Philippines, Quezon City

2. FLUID MECHANICS
• Fluid Statics
– Study of fluids at rest in equilibrium situations.
• Fluid Dynamics
– Study of fluids in motion.

3. FLUIDS
• Any substance that is free-flowing.
• Include liquids and gases.
• Non-rigid bodies.

4. DENSITY
•M a s s p e r u n i t
v o l u me
•C o n s t a n t f o r
e v e r y s u b s t a n c e
•S I U N I T = k g /m 3
m
V

6. • Wh i c h h a s a
g r e a t e r De n s i t y ?
Go l d B a r
Go l d Ri n g

7. Specific Gravity (“Relative Density”)
•Ratio of a material’s density to the
density of water at 4 oC.
ρwater @ 4 °C = 1000 kg/m3 = 1 g/cm3
Specific Gravity = Material
Water

10. Fluid Pressure
•Force per unit Area
dF
dP
dA
•If Pressure is constant
throughout the area.
F
P
A

11. HYDROSTATIC EQUILIBRIUM
• Net force on the fluid is zero
• i.e. Equal pressures on opposite directions.
• i.e. Pressure difference gives rise to a net force.

12. Atmospheric Pressure (Patm)
• Example of compressive fluid pressure.
• Due to the Earth’s atmosphere.
• Roughly constant near the surface of the earth.
Patm 1atm 1.013 bar 14 .7 psi

14. PRESSURE DEPENDENCE
• Pressure varies with depth.
• Assumption:
• Density is constant.
• Acceleration due to gravity is
constant.
• Fluid is in equilibrium.

15. PRESSURE DEPENDENCE

16. Fy 0
PA (P dP)A dW 0
Recall : dW dmg;dm ρdV; dV Ady
Therefore: dW ρdVg ρAgdy
So :
PA (P dP) ρgdy 0
P P dP ρgdy 0
dP ρgdy
dP
ρg
dy

17. PRESSURE DEPENDENCE
In a fluid of constant density, take two points
p, at y1, from the bottom and p2 at y2 from
the bottom:
dP ρgdy To Generalize:
po y2
p = po + ρgh
dP ρgdy
p y1
p 2 p1 ρg(y2 y1 )
p 2 p1 ρgh
p1 p 2 ρgh

18. Measured from below the
surface; upward
positive.
Measured from the
surface; downward
negative
Measured from the
surface; downward
positive

19. The pressure p at a depth h is greater than the
pressure po at the same level in the fluid.

20. • Gauge Pressure
– Excess pressure above the atmospheric pressure.
p gauge p p atm
• Absolute Pressure
– Actual Pressure

21. PASCAL’S PRINCIPLE
• “Pressure applied to an enclosed fluid is transmitted
undiminished to every portion of the fluid and the
walls of the containing vessel.
Hydraulic Lift
F1 F2
p
A2 A2

22. PRESSURE GAUGES
Open-tube Manometer
•The U-shaped tube contains a liquid
often water or mercury.
•Left end is connected to a container
where the pressure will be
measured
•Right end is open to the atmosphere.
p ρgy patm ρgy2
p patm ρg(y2 y1 ) ρgh

24. PRESSURE GAUGES
• Mercury Barometer
• Of a long glass tube, closed
at one end, that has to filled
with mercury and then
inverted in a dish of mercury.
• Space above the mercury
column contains mercury
vapor (pressure is very
small).
• The mercury barometer
reads the atmospheric
pressure directly from the
height of the mercury
column

25. Ans. 1.9×104 N

26. Ans. 1.05×105 Pa

27. Ans. (a). 7.322×10−3 kg (b). VAu = 3.79×10−7 m3 , VCu = 7.46×10−8 m3 (c). 1.76×104kg/m3

28. Thank You Very Much!!!