Lecture 3 Flashcards
floating object mass
mass of object= mass of fluid displaced
submerged object volume
volume of object equals volume of fluid displaced
Specific gravity
density of substance compared to density of water
Specific gravity <1
substance is lighter than water
density of water
1000 kg m3= 1g/cm3
Pascals principle
pressure applied anywhere in an enclosed incompressible fluid will be distributed undiminished throughout the fluid
absolute pressure
pressure of system relative to a vacuum
Pab= Pguage + Patm
gauge pressure
amount by which a systems. pressure deviates from atmospheric pressure
hydraulic lift
2 pistons with a container containing incompressible liquid. Force on piston 1 applied pressure and is transferred to piston 2
Piston 2 has greater area so it has greater force (P is constant)
Pascals
Buoyant force
fluid exerting force on an object that is in fluid
Pressure and force increases as depth increases.
Different pressure and force at different depth= increased Buoyant force
When is buoyant force high
when the object is fully submerged
Buoyancy equation
Fb= (Density fluid) (V fluid) g
Fb= mass of fluid * g
Archimedes principle
upward buoyant force is equal in magnitude to the eight of displaced fluid
Floating object forces
displaces volume of fluid with mass equal to its own mass
Fb= gravitational force (weight)
weight object is cancelled by weight of fluid displaced
Fraction of object submerged when floating
V fluid/ V object
density object/ density fluid
equals Specific gravity
submerged object forces
displaced a volume of fluid equal to its own volume, experiences an upward Fb equal to Gravitational force
V fluid and depth are at max
m object= m fluid, V fluid= V object
(Fraction of object submerged= 1- equal density)
Sunk object forces
Fb is smaller than downward gravitational force
displaced volume equal to own object volume
M fluid < M object, V fluid= V object
Object is denser
Fb + FN = Fg= M object G
Weight loss of sunken object
density fluid / density object x 100%
floating object equation
Fb= M(fluid)g = Fg= M(object) g
Ideal fluid traits
- no viscosity
- incompressible with uniform density
- lack turbulence (steady, laminar flow, same velocity at any point)
- have irrotational flow ( does not rotate as it flows)
What does the continuity equation mean
volume is constant, and equals A*d
same volume flows through in a given time, it has a rate equal to Q
Narrow pipe= greater velocity
Continuity equation
Q= Av
Q= volume flow rate
v=velocity= d/t
Mass flow rate
I= density (Q) = density(A)(v)
stream lines
show ideal fluid
velocity is tangent to line
closer streamlines means greater velocity
Bernoullis equation
p1+(1/2ρv1^2)+ρgh1 =p2+(1/2ρv2^2)+ ρgh2
h= distance above arbitrary point
Velocity of fluid from a spigot
V= sqrt (2gh)
Pitot tube
u shaped tube. Opening 1 has velocity= 0, pressure=static
opening 2 has moving fluid, pressure= total fluid pressure
shows velocity of fluid moving around it
venturi tube
horizontal tube with constricted region
shows velocity of fluid flowing in it
decreased A means increased V, decrease in pressure
Venturi effect
decrease in pressure when fluid flows through constricted pie
pitot tube equation
h1=h2, v1=0, so
P2+ 1/2ρv2^2= P1
Real fluid characteristics
velocity is greatest at center of the pipe
resistance to flow increases as length of pipe increases, more narrow= more drag effect (volume effect)
Volume= pi r^2 d
Real fluid flow
delta p= QR
fluid flows high to low pressure
Poiseuilles Law
Q= delta P [(pi r^4)/ 8 nL]
n= viscosity, L= pipe length
for horizontal pipe with constant area
increase in radius can increase flow rate
How does velocity change with radius
smaller radius means increase in velocity
Surface tension
intensity of intermolecular force of fluid per length
higher temperature means weaker tension
cohesive vs. adhesive forces
cohesive act in surface tension, adhesive act between a tube and fluid molecules
concave vs convex
concave is when adhesive forces are stronger (fluid pulled upward at end)
in convex, cohesive is stronger (fluid pulled downward at ends)
