Post on 19-May-2015
MECHANICS OF FLUIDS
FLUIDS
Anything that can flowLiquid and Gases
Fluid DynamicsFluid Static- Study of fluids in motion
- study of fluids at rest
Density- ratio of mass of a substance to its volume
V
m
= densitym = massV = volume
Unit: kg/m3
Density
When the can is squeezed, the density increases.
What will happen to its density?
Density
Pressure- force per unit area
A
FP
P = pressureF = forceA = area
Unit: N/m2 or Pa
Pressure
Pressure
PressureIt is the same any particular depth in liquid contained in vessels of different sizes or shape.
12 Pa
12 Pa
12 Pa
1. Pascal’s Principle
The pressure applied at any given point on a confined fluid is transmitted undiminished throughout the fluid.
Application
1. Pascal’s Principle
The pressure applied at any given point on a confined fluid is transmitted undiminished throughout the fluid.
Application
This is much better!
1. Pascal’s Principle
The pressure applied at any given point on a confined fluid is transmitted undiminished throughout the fluid.
2
2
1
1
21
A
F
A
F
PP
1. Pascal’s Principle
F1 = 2500 N F2 = ? W = 10000 NA1 = 2 m2 A2 = 8 m2
2
2
1
1
21
A
F
A
F
PP
2. Bernoulli’s Principle
- As the velocity of the fluid increases, its pressure decreases
BuoyancyThe fluid always go from high pressure area to low pressure
area
What will happen if the train passes on your side?
Lower velocityHigher pressure
Higher velocityLower pressure
Buoyancy
- upward force when object is submerge in fluid
Buoyant force
3. Archimedes’ Principle
A body partly or entire submerged in a fluid is buoyed up by a force equal in magnitude to the weight of the displaced fluid.
BF = Wair - Wwater
BF = Wfluid displaced
Problems1. An 80 kg metal cylinder 2m long and with each end of area 25 cm2 stands vertically on one end. What pressure does the cylinder exert on the floor?
2. A piston of cross-sectional area "a" is used in a hydraulic press to exert a small force of magnitude "f" on the enclosed liquid. A connecting pipe leads to a larger piston of cross-sectional area A. If the piston diameters are 3.80 cm and 53.0 cm, what force magnitude on the small piston will balance a 20.0 kN force on the large piston?
Problems
3. What is the maximum weight a solid, square, pinewood raft measuring 4.0 m on a side and 0.30 m thick support and still float in water? How much weight can we add in the raft so that it can still float? wood = 420 kg/m3
4. A solid aluminum cylinder, = 2700 kg/m3 weighs 0.067 kg in air and 0.045 kg in turpentine. Determine the density of the turpentine.